[compiler-rt] Moved cmake libatomic check to top level config-ix (#99437)

Also add atomic check to rtsan for when the tests are merged (related
review #98679)

Author: cjappl

compiler-rt/cmake/config-ix.cmake

@@ -176,6 +176,7 @@ check_cxx_compiler_flag(-nostdlib++ COMPILER_RT_HAS_NOSTDLIBXX_FLAG)
 check_include_files("sys/auxv.h"    COMPILER_RT_HAS_AUXV)
 
 # Libraries.
+check_library_exists(atomic __atomic_load_8 "" COMPILER_RT_HAS_LIBATOMIC)
 check_library_exists(dl dlopen "" COMPILER_RT_HAS_LIBDL)
 check_library_exists(rt shm_open "" COMPILER_RT_HAS_LIBRT)
 check_library_exists(m pow "" COMPILER_RT_HAS_LIBM)

compiler-rt/lib/rtsan/tests/CMakeLists.txt

@@ -36,6 +36,7 @@ set(RTSAN_UNITTEST_LINK_FLAGS
   ${SANITIZER_TEST_CXX_LIBRARIES}
   -no-pie)
 
+append_list_if(COMPILER_RT_HAS_LIBATOMIC -latomic RTSAN_UNITTEST_LINK_FLAGS)
 append_list_if(COMPILER_RT_HAS_LIBDL -ldl RTSAN_UNITTEST_LINK_FLAGS)
 append_list_if(COMPILER_RT_HAS_LIBRT -lrt RTSAN_UNITTEST_LINK_FLAGS)
 append_list_if(COMPILER_RT_HAS_LIBM -lm RTSAN_UNITTEST_LINK_FLAGS)

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

@@ -46,11 +46,8 @@ set(SCUDO_UNITTEST_LINK_FLAGS
   ${COMPILER_RT_UNWINDER_LINK_LIBS}
   ${SANITIZER_TEST_CXX_LIBRARIES})
 list(APPEND SCUDO_UNITTEST_LINK_FLAGS -pthread -no-pie)
-# Linking against libatomic is required with some compilers
-check_library_exists(atomic __atomic_load_8 "" COMPILER_RT_HAS_LIBATOMIC)
-if (COMPILER_RT_HAS_LIBATOMIC)
-  list(APPEND SCUDO_UNITTEST_LINK_FLAGS -latomic)
-endif()
+
+append_list_if(COMPILER_RT_HAS_LIBATOMIC -latomic SCUDO_UNITTEST_LINK_FLAGS)
 
 set(SCUDO_TEST_HEADERS
   scudo_unit_test.h