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

This isn't needed anymore.

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

Author: petrhosek

runtimes/CMakeLists.txt

@@ -103,36 +103,38 @@ 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.
-  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 "${CMAKE_REQUIRED_FLAGS}")
-    set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} --unwindlib=none")
-    # TODO: When we can require CMake 3.14, we should use
-    # CMAKE_REQUIRED_LINK_OPTIONS here. Until then, we need a workaround:
-    # When using CMAKE_REQUIRED_FLAGS, this option gets added both to
-    # compilation and linking commands. That causes warnings in the
-    # compilation commands during cmake tests. This is normally benign, but
-    # when testing whether -Werror works, that test fails (due to the
-    # preexisting warning).
-    #
-    # Therefore, before we can use CMAKE_REQUIRED_LINK_OPTIONS, check if we
-    # can use --start-no-unused-arguments to silence the warnings about
-    # --unwindlib=none during compilation.
-    #
-    # We must first add --unwindlib=none to CMAKE_REQUIRED_FLAGS above, to
-    # allow this subsequent test to succeed, then rewrite CMAKE_REQUIRED_FLAGS
-    # below.
-    check_c_compiler_flag("--start-no-unused-arguments" C_SUPPORTS_START_NO_UNUSED_ARGUMENTS)
-    if (C_SUPPORTS_START_NO_UNUSED_ARGUMENTS)
-      set(CMAKE_REQUIRED_FLAGS "${ORIG_CMAKE_REQUIRED_FLAGS} --start-no-unused-arguments --unwindlib=none --end-no-unused-arguments")
-    endif()
+# The compiler driver may be implicitly trying to link against libunwind,
+# which might not work if libunwind doesn't exist yet. Try to check if
+# --unwindlib=none is supported, and use that if possible.
+#
+# TODO: Note that this is problematic when LLVM_USE_SANITIZER is used
+# because some sanitizers require the unwinder and so the combination of
+# -fsanitize=... --unwindlib=none will always result in a linking error.
+# Currently, we counteract this issue by adding -fno-sanitize=all flag in
+# the project specific code within */cmake/config-ix.cmake files but that's
+# brittle. We should ideally move this to runtimes/CMakeLists.txt.
+llvm_check_compiler_linker_flag(C "--unwindlib=none" CXX_SUPPORTS_UNWINDLIB_EQ_NONE_FLAG)
+if (CXX_SUPPORTS_UNWINDLIB_EQ_NONE_FLAG)
+  set(ORIG_CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
+  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} --unwindlib=none")
+  # TODO: When we can require CMake 3.14, we should use
+  # CMAKE_REQUIRED_LINK_OPTIONS here. Until then, we need a workaround:
+  # When using CMAKE_REQUIRED_FLAGS, this option gets added both to
+  # compilation and linking commands. That causes warnings in the
+  # compilation commands during cmake tests. This is normally benign, but
+  # when testing whether -Werror works, that test fails (due to the
+  # preexisting warning).
+  #
+  # Therefore, before we can use CMAKE_REQUIRED_LINK_OPTIONS, check if we
+  # can use --start-no-unused-arguments to silence the warnings about
+  # --unwindlib=none during compilation.
+  #
+  # We must first add --unwindlib=none to CMAKE_REQUIRED_FLAGS above, to
+  # allow this subsequent test to succeed, then rewrite CMAKE_REQUIRED_FLAGS
+  # below.
+  check_c_compiler_flag("--start-no-unused-arguments" C_SUPPORTS_START_NO_UNUSED_ARGUMENTS)
+  if (C_SUPPORTS_START_NO_UNUSED_ARGUMENTS)
+    set(CMAKE_REQUIRED_FLAGS "${ORIG_CMAKE_REQUIRED_FLAGS} --start-no-unused-arguments --unwindlib=none --end-no-unused-arguments")
   endif()
 endif()