cfltk tries to link with libfltk.a when building shared libs

[khacng]

I built cfltk with CFLTK_BUILD_SHARED=ON and it tried to link with libfltk.a instead of libfltk.so. Here's the log:

/sbin/ld: /usr/local/lib64/libfltk.a(Fl_Message.cxx.o): warning: relocation against FL_NORMAL_SIZE' in read-only section .text'
/sbin/ld: /usr/local/lib64/libfltk.a(Fl.cxx.o): relocation R_X86_64_PC32 against symbol `_ZN16Fl_Screen_Driver13system_driverE' can not be used when making a shared object; recompile with -fPIC
/sbin/ld: final link failed: bad value
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/cfltk.dir/build.make:485: libcfltk.so.1.4.5] Error 1
make[1]: *** [CMakeFiles/Makefile2:83: CMakeFiles/cfltk.dir/all] Error 2
make: *** [Makefile:136: all] Error 2

[MoAlyousef]

CFLTK_BUILD_SHARED creates a standalone libcfltk.so library which no longer needs libfltk.so.
See here:
#184 (comment)