[runtimes][CMake] Drop the check to see if linker works

This isn't needed anymore.

Differential Revision: https://reviews.llvm.org/D144440

runtimes/CMakeLists.txt

@@ -103,13 +103,16 @@ filter_prefixed("${CMAKE_C_IMPLICIT_INCLUDE_DIRECTORIES}" ${LLVM_BINARY_DIR} CMA
 filter_prefixed("${CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES}" ${LLVM_BINARY_DIR} CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES)
 filter_prefixed("${CMAKE_ASM_IMPLICIT_INCLUDE_DIRECTORIES}" ${LLVM_BINARY_DIR} CMAKE_ASM_IMPLICIT_INCLUDE_DIRECTORIES)
 
-check_c_compiler_flag("" LLVM_RUNTIMES_LINKING_WORKS)
-if (NOT LLVM_RUNTIMES_LINKING_WORKS)
 # The compiler driver may be implicitly trying to link against libunwind,
 # which might not work if libunwind doesn't exist yet. Try to check if
 # --unwindlib=none is supported, and use that if possible.
-  # Don't add this if not necessary to fix linking, as it can break using
-  # e.g. ASAN/TSAN.
+#
+# TODO: Note that this is problematic when LLVM_USE_SANITIZER is used
+# because some sanitizers require the unwinder and so the combination of
+# -fsanitize=... --unwindlib=none will always result in a linking error.
+# Currently, we counteract this issue by adding -fno-sanitize=all flag in
+# the project specific code within */cmake/config-ix.cmake files but that's
+# brittle. We should ideally move this to runtimes/CMakeLists.txt.
 llvm_check_compiler_linker_flag(C "--unwindlib=none" CXX_SUPPORTS_UNWINDLIB_EQ_NONE_FLAG)
 if (CXX_SUPPORTS_UNWINDLIB_EQ_NONE_FLAG)
   set(ORIG_CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
@@ -134,7 +137,6 @@ if (NOT LLVM_RUNTIMES_LINKING_WORKS)
     set(CMAKE_REQUIRED_FLAGS "${ORIG_CMAKE_REQUIRED_FLAGS} --start-no-unused-arguments --unwindlib=none --end-no-unused-arguments")
   endif()
 endif()
-endif()
 
 # Disable use of the installed C++ standard library when building runtimes.
 # Check for -nostdlib++ first; if there's no C++ standard library yet,