[compiler-rt] Fix scudo build on ARM

The build of scudo was failing on armv7l, with undefined references
to unwinder symbols, such as __aeabi_unwind_cpp_pr0. These are
needed by RTGwpAsan and thus, on ARM, scudo must also be linked
against an unwind library.

The cmake command that caused the build failure was:

cmake --fresh -S "$PWD/llvm/" -B "$PWD/build/" -G Ninja \
  -DCMAKE_INSTALL_PREFIX="$PWD/install" \
  -DCMAKE_BUILD_TYPE=Release \
  -DLLVM_ENABLE_PROJECTS="clang;lld;lldb;clang-tools-extra;polly" \
  -DLLVM_ENABLE_RUNTIMES="compiler-rt;libcxx;libcxxabi;libunwind" \
  -DLLVM_TOOLCHAIN_TOOLS="llvm-ar;llvm-ranlib;llvm-objdump;\
llvm-rc;llvm-cvtres;llvm-nm;llvm-strings;llvm-readobj;\
llvm-dlltool;llvm-pdbutil;llvm-objcopy;llvm-strip;llvm-cov;\
llvm-profdata;llvm-addr2line;llvm-symbolizer;llvm-windres;llvm-ml;\
llvm-readelf;llvm-size" \
  -DLLVM_INSTALL_BINUTILS_SYMLINKS=OFF -DLLVM_PARALLEL_LINK_JOBS=1

Fixes llvm#60115

Reviewed By: hctim

Differential Revision: https://reviews.llvm.org/D142888

compiler-rt/lib/scudo/standalone/CMakeLists.txt

@@ -138,8 +138,19 @@ set(SCUDO_SOURCES_CXX_WRAPPERS
   )
 
 set(SCUDO_OBJECT_LIBS)
+set(SCUDO_LINK_LIBS)
 
 if (COMPILER_RT_HAS_GWP_ASAN)
+  if(COMPILER_RT_USE_LLVM_UNWINDER)
+    list(APPEND SCUDO_LINK_LIBS ${COMPILER_RT_UNWINDER_LINK_LIBS} dl)
+  elseif (COMPILER_RT_HAS_GCC_S_LIB)
+    list(APPEND SCUDO_LINK_LIBS gcc_s)
+  elseif (COMPILER_RT_HAS_GCC_LIB)
+    list(APPEND SCUDO_LINK_LIBS gcc)
+  else()
+    message(FATAL_ERROR "No suitable unwinder library")
+  endif()
+
   add_dependencies(scudo_standalone gwp_asan)
   list(APPEND SCUDO_OBJECT_LIBS
        RTGwpAsan RTGwpAsanBacktraceLibc RTGwpAsanSegvHandler
@@ -152,8 +163,6 @@ if (COMPILER_RT_HAS_GWP_ASAN)
 
 endif()
 
-set(SCUDO_LINK_LIBS ${COMPILER_RT_UNWINDER_LINK_LIBS})
-
 if(COMPILER_RT_BUILD_SCUDO_STANDALONE_WITH_LLVM_LIBC)
   include_directories(${COMPILER_RT_BINARY_DIR}/../libc/include/)