[compiler-rt][CMake] Use linker semantics for unwinder and C++ library

[phosek]

Summary

Try the shared library first, and if it doesn't exist fallback onto
the static one. When the static library is requested, skip the shared
library.

compiler-rt/CMakeLists.txt

 
 # When cross-compiling, COMPILER_RT_TEST_COMPILER_CFLAGS help in compilation
 # and linking of unittests.
 string(REPLACE " " ";" COMPILER_RT_UNITTEST_CFLAGS "${COMPILER_RT_TEST_COMPILER_CFLAGS}")
 set(COMPILER_RT_UNITTEST_LINK_FLAGS ${COMPILER_RT_UNITTEST_CFLAGS})
 
 if(COMPILER_RT_USE_LLVM_UNWINDER)
   if (COMPILER_RT_ENABLE_STATIC_UNWINDER)
-    set(unwinder_target unwind_static)
+    list(APPEND SANITIZER_CXX_ABI_LIBRARIES "$<TARGET_LINKER_FILE:unwind_static>")
   else()
-    set(unwinder_target unwind_shared)
+    list(APPEND SANITIZER_CXX_ABI_LIBRARIES "$<TARGET_LINKER_FILE:$<IF:$<TARGET_EXISTS:unwind_shared>,unwind_shared,unwind_static>>")
   endif()
-  list(APPEND SANITIZER_CXX_ABI_LIBRARIES "$<$<TARGET_EXISTS:${unwinder_target}>:$<TARGET_LINKER_FILE:${unwinder_target}>>")
 endif()
 
 if (COMPILER_RT_CXX_LIBRARY STREQUAL "libcxx")
   # We are using the in-tree libc++ so avoid including the default one.
   append_list_if(COMPILER_RT_HAS_NOSTDINCXX_FLAG -nostdinc++ COMPILER_RT_COMMON_CFLAGS)
   append_list_if(COMPILER_RT_HAS_NOSTDLIBXX_FLAG -nostdlib++ COMPILER_RT_COMMON_LINK_FLAGS)
   # Use the in-tree libc++ through explicit include and library paths.
+  set(COMPILER_RT_CXX_CFLAGS "$<$<TARGET_EXISTS:cxx-headers>:-isystem$<JOIN:$<TARGET_PROPERTY:cxx-headers,INTERFACE_INCLUDE_DIRECTORIES>,$<SEMICOLON>-isystem>>")
   if (COMPILER_RT_STATIC_CXX_LIBRARY)
-    set(cxx_target cxx_static)
+    set(COMPILER_RT_CXX_LINK_LIBS "$<TARGET_LINKER_FILE:cxx_static>")
   else()
-    set(cxx_target cxx_shared)
+    set(COMPILER_RT_CXX_LINK_LIBS "$<TARGET_LINKER_FILE:$<IF:$<TARGET_EXISTS:cxx_shared>,cxx_shared,cxx_static>>")
   endif()
-  list(APPEND COMPILER_RT_CXX_CFLAGS "$<$<TARGET_EXISTS:cxx-headers>:-isystem$<JOIN:$<TARGET_PROPERTY:cxx-headers,INTERFACE_INCLUDE_DIRECTORIES>,$<SEMICOLON>-isystem>>")
-  list(APPEND COMPILER_RT_CXX_LINK_LIBS "$<$<TARGET_EXISTS:${cxx_target}>:$<TARGET_LINKER_FILE:${cxx_target}>>")
 elseif (COMPILER_RT_CXX_LIBRARY STREQUAL "none")
   # We aren't using any C++ standard library so avoid including the default one.
   append_list_if(COMPILER_RT_HAS_NOSTDINCXX_FLAG -nostdinc++ COMPILER_RT_COMMON_CFLAGS)
   append_list_if(COMPILER_RT_HAS_NOSTDLIBXX_FLAG -nostdlib++ COMPILER_RT_COMMON_LINK_FLAGS)
 else()
   # Nothing to be done for `default`.
 endif()
 

 elseif (SANITIZER_CXX_ABI_LIBNAME STREQUAL "libcxxabi")
   list(APPEND SANITIZER_CXX_ABI_LIBRARIES "c++abi")
 elseif (SANITIZER_CXX_ABI_LIBNAME STREQUAL "libstdc++")
   append_list_if(COMPILER_RT_HAS_LIBSTDCXX stdc++ SANITIZER_CXX_ABI_LIBRARIES)
 endif()
 
 if (SANITIZER_TEST_CXX_LIBNAME STREQUAL "libc++")
   if (SANITIZER_TEST_CXX_INTREE)
+    list(APPEND SANITIZER_TEST_CXX_CFLAGS "$<$<TARGET_EXISTS:cxx-headers>:-isystem$<JOIN:$<TARGET_PROPERTY:cxx-headers,INTERFACE_INCLUDE_DIRECTORIES>,$<SEMICOLON>-isystem>>")
     if (SANITIZER_USE_STATIC_TEST_CXX)
-      set(cxx_target cxx_static)
+      list(APPEND SANITIZER_TEST_CXX_LIBRARIES "$<TARGET_LINKER_FILE:cxx_static>")
     else()
-      set(cxx_target cxx_shared)
+      list(APPEND SANITIZER_TEST_CXX_LIBRARIES "$<TARGET_LINKER_FILE:$<IF:$<TARGET_EXISTS:cxx_shared>,cxx_shared,cxx_static>>")
     endif()
-    list(APPEND SANITIZER_TEST_CXX_LIBRARIES "$<$<TARGET_EXISTS:${cxx_target}>:$<TARGET_LINKER_FILE:${cxx_target}>>")
-    list(APPEND SANITIZER_TEST_CXX_CFLAGS "$<$<TARGET_EXISTS:cxx-headers>:-isystem$<JOIN:$<TARGET_PROPERTY:cxx-headers,INTERFACE_INCLUDE_DIRECTORIES>,$<SEMICOLON>-isystem>>")
     # We are using the in tree libc++ so avoid including the default one.
     append_list_if(COMPILER_RT_HAS_NOSTDINCXX_FLAG -nostdinc++ COMPILER_RT_UNITTEST_CFLAGS)
     append_list_if(COMPILER_RT_HAS_NOSTDLIBXX_FLAG -nostdlib++ COMPILER_RT_UNITTEST_LINK_FLAGS)
   else()
     append_list_if(COMPILER_RT_HAS_LIBCXX -lc++ SANITIZER_TEST_CXX_LIBRARIES)
   endif()
 elseif (SANITIZER_TEST_CXX_LIBNAME STREQUAL "libstdc++")
   append_list_if(COMPILER_RT_HAS_LIBSTDCXX -lstdc++ SANITIZER_TEST_CXX_LIBRARIES)