-Werror=unused-result in GCC48 compiler

[luotao1]

When use GCC48 to compile mkldnn, there are a lot of -Werror=unused-result errors. But when use GCC53, there is no error.

• configuration:

[14:59:21] :	 [Step 1/4] -- Found Paddle host system: centos, version: 6.9
[14:59:21] :	 [Step 1/4] -- Found Paddle host system's CPU: 12 cores
[14:59:22] :	 [Step 1/4] -- The CXX compiler identification is GNU 4.8.2
[14:59:22] :	 [Step 1/4] -- The C compiler identification is GNU 4.8.2

• error log:

In file included from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/cpu_barrier.hpp:22:0,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/cpu_barrier.cpp:19:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp: In member function ‘void mkldnn::impl::cpu::jit_generator::dump_code(const uint8*) const’:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp:719:47: error: ignoring return value of ‘size_t fwrite(const void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]
                 fwrite(code, getSize(), 1, fp);
                                               ^
cc1plus: all warnings being treated as errors
make[5]: *** [src/CMakeFiles/mkldnn.dir/cpu/cpu_barrier.cpp.o] Error 1
make[5]: *** Waiting for unfinished jobs....
In file included from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_uni_dw_conv_kernel_f32.hpp:21:0,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_uni_dw_conv_kernel_f32.cpp:23:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp: In member function ‘void mkldnn::impl::cpu::jit_generator::dump_code(const uint8*) const’:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp:719:47: error: ignoring return value of ‘size_t fwrite(const void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]
                 fwrite(code, getSize(), 1, fp);
                                               ^
In file included from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_transpose_src_utils.cpp:21:0:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp: In member function ‘void mkldnn::impl::cpu::jit_generator::dump_code(const uint8*) const’:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp:719:47: error: ignoring return value of ‘size_t fwrite(const void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]
                 fwrite(code, getSize(), 1, fp);
                                               ^
In file included from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_uni_reorder.cpp:29:0:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp: In member function ‘void mkldnn::impl::cpu::jit_generator::dump_code(const uint8*) const’:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp:719:47: error: ignoring return value of ‘size_t fwrite(const void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]
                 fwrite(code, getSize(), 1, fp);
                                               ^
cc1plus: all warnings being treated as errors
make[5]: *** [src/CMakeFiles/mkldnn.dir/cpu/jit_transpose_src_utils.cpp.o] Error 1
cc1plus: all warnings being treated as errors
make[5]: *** [src/CMakeFiles/mkldnn.dir/cpu/jit_uni_reorder.cpp.o] Error 1
In file included from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/cpu_barrier.hpp:22:0,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/cpu_reducer.hpp:28,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx2_convolution.hpp:23,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx2_convolution.cpp:20:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp: In member function ‘void mkldnn::impl::cpu::jit_generator::dump_code(const uint8*) const’:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp:719:47: error: ignoring return value of ‘size_t fwrite(const void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]
                 fwrite(code, getSize(), 1, fp);
                                               ^
cc1plus: all warnings being treated as errors
In file included from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/cpu_barrier.hpp:22:0,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/cpu_reducer.hpp:28,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx512_common_1x1_convolution.hpp:23,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx512_common_1x1_convolution.cpp:20:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp: In member function ‘void mkldnn::impl::cpu::jit_generator::dump_code(const uint8*) const’:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp:719:47: error: ignoring return value of ‘size_t fwrite(const void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]
                 fwrite(code, getSize(), 1, fp);
                                               ^
make[5]: *** [src/CMakeFiles/mkldnn.dir/cpu/jit_uni_dw_conv_kernel_f32.cpp.o] Error 1
In file included from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx512_common_conv_winograd_kernel_f32.hpp:23:0,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx512_common_convolution_winograd.hpp:25,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx512_core_convolution_winograd.cpp:28:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp: In member function ‘void mkldnn::impl::cpu::jit_generator::dump_code(const uint8*) const’:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp:719:47: error: ignoring return value of ‘size_t fwrite(const void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]
                 fwrite(code, getSize(), 1, fp);
                                               ^
In file included from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/cpu_barrier.hpp:22:0,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/cpu_reducer.hpp:28,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx2_1x1_convolution.hpp:23,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx2_1x1_convolution.cpp:20:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp: In member function ‘void mkldnn::impl::cpu::jit_generator::dump_code(const uint8*) const’:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp:719:47: error: ignoring return value of ‘size_t fwrite(const void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]
                 fwrite(code, getSize(), 1, fp);
                                               ^
cc1plus: all warnings being treated as errors
make[5]: *** [src/CMakeFiles/mkldnn.dir/cpu/jit_avx2_convolution.cpp.o] Error 1
cc1plus: all warnings being treated as errors
cc1plus: all warnings being treated as errors
make[5]: *** [src/CMakeFiles/mkldnn.dir/cpu/jit_avx512_core_convolution_winograd.cpp.o] Error 1
make[5]: *** [src/CMakeFiles/mkldnn.dir/cpu/jit_avx512_common_1x1_convolution.cpp.o] Error 1
In file included from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_uni_batch_normalization.cpp:26:0:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp: In member function ‘void mkldnn::impl::cpu::jit_generator::dump_code(const uint8*) const’:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp:719:47: error: ignoring return value of ‘size_t fwrite(const void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]
                 fwrite(code, getSize(), 1, fp);
                                               ^
cc1plus: all warnings being treated as errors
In file included from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx512_core_u8s8s32x_1x1_convolution.cpp:23:0:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp: In member function ‘void mkldnn::impl::cpu::jit_generator::dump_code(const uint8*) const’:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp:719:47: error: ignoring return value of ‘size_t fwrite(const void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]
                 fwrite(code, getSize(), 1, fp);
                                               ^
make[5]: *** [src/CMakeFiles/mkldnn.dir/cpu/jit_avx2_1x1_convolution.cpp.o] Error 1
cc1plus: all warnings being treated as errors
make[5]: *** [src/CMakeFiles/mkldnn.dir/cpu/jit_uni_batch_normalization.cpp.o] Error 1
cc1plus: all warnings being treated as errors
make[5]: *** [src/CMakeFiles/mkldnn.dir/cpu/jit_avx512_core_u8s8s32x_1x1_convolution.cpp.o] Error 1
In file included from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_uni_eltwise.cpp:22:0:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp: In member function ‘void mkldnn::impl::cpu::jit_generator::dump_code(const uint8*) const’:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp:719:47: error: ignoring return value of ‘size_t fwrite(const void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]
                 fwrite(code, getSize(), 1, fp);
                                               ^
In file included from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx2_gemm_f32.hpp:21:0,
                 from /home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_avx2_gemm_f32.cpp:22:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp: In member function ‘void mkldnn::impl::cpu::jit_generator::dump_code(const uint8*) const’:
/home/luotao02/Paddle/build/third_party/mkldnn/src/extern_mkldnn/src/cpu/jit_generator.hpp:719:47: error: ignoring return value of ‘size_t fwrite(const void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Werror=unused-result]
                 fwrite(code, getSize(), 1, fp);
                                               ^
cc1plus: all warnings being treated as errors
make[5]: *** [src/CMakeFiles/mkldnn.dir/cpu/jit_avx2_gemm_f32.cpp.o] Error 1
cc1plus: all warnings being treated as errors
make[5]: *** [src/CMakeFiles/mkldnn.dir/cpu/jit_uni_eltwise.cpp.o] Error 1
make[4]: *** [src/CMakeFiles/mkldnn.dir/all] Error 2
make[3]: *** [all] Error 2
make[2]: *** [third_party/mkldnn/src/extern_mkldnn-stamp/extern_mkldnn-build] Error 2
make[1]: *** [CMakeFiles/extern_mkldnn.dir/all] Error 2
make: *** [all] Error 2

• whole log: https://paddleci.ngrok.io/viewLog.html?buildId=35590&buildTypeId=Manylinux1_Cuda80cudnn5cp27cp27mu&tab=buildLog&_focus=3589
• related issue: mkldnn compiler error in gcc48 PaddlePaddle/Paddle#10584

Now we use -Wno-error=unused-result -Wno-unused-result to skip this error in PaddlePaddle/Paddle#10571. But could you help fix it at all? Thanks very much!