[libcxx] cmake - guard list remove
REMOVE_ITEM fails if CMAKE_REQUIRED_LIBRARIES is empty on some
versions of cmake.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@359755 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/cmake/Modules/CheckLibcxxAtomic.cmake b/cmake/Modules/CheckLibcxxAtomic.cmake
index 1e6e5e6..7fe5a62 100644
--- a/cmake/Modules/CheckLibcxxAtomic.cmake
+++ b/cmake/Modules/CheckLibcxxAtomic.cmake
@@ -34,10 +34,12 @@
# Perform the check for 64bit atomics without libatomic. It may have been
# added to the required libraries during in the configuration of LLVM, which
# would cause the check for CXX atomics without libatomic to incorrectly pass.
-set(OLD_CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
-list(REMOVE_ITEM CMAKE_REQUIRED_LIBRARIES "atomic")
-check_cxx_atomics(LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB)
-set(CMAKE_REQUIRED_LIBRARIES ${OLD_CMAKE_REQUIRED_LIBRARIES})
+if (CMAKE_REQUIRED_LIBRARIES)
+ set(OLD_CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
+ list(REMOVE_ITEM CMAKE_REQUIRED_LIBRARIES "atomic")
+ check_cxx_atomics(LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB)
+ set(CMAKE_REQUIRED_LIBRARIES ${OLD_CMAKE_REQUIRED_LIBRARIES})
+endif()
check_library_exists(atomic __atomic_fetch_add_8 "" LIBCXX_HAS_ATOMIC_LIB)
# If not, check if the library exists, and atomics work with it.
