Sourced from https://bugs.webkit.org/show_bug.cgi?id=161900

on arm fixes

| /usr/src/debug/libgcc/6.2.0-r0/gcc-6.2.0/build.arm-oe-linux-gnueabi.arm-oe-linux-gnueabi/libgcc/../../../../../../../work-shared/gcc-6.2.0-r0/gcc-6.2.0/libgcc/config/arm/linux-atomic-64bit.c:117: multiple definition of `__sync_sub_and_fetch_8'

Signed-off-by: Khem Raj <raj.khem@gmail.com>

Upstream-Status: Backport

diff --git a/Source/WTF/wtf/CMakeLists.txt b/Source/WTF/wtf/CMakeLists.txt
index 867999e..ea69322 100644
--- a/Source/WTF/wtf/CMakeLists.txt
+++ b/Source/WTF/wtf/CMakeLists.txt
@@ -171,7 +171,6 @@ set(WTF_HEADERS
 
 set(WTF_SOURCES
     Assertions.cpp
-    Atomics.cpp
     BitVector.cpp
     CompilationThread.cpp
     CrossThreadCopier.cpp
@@ -276,6 +275,15 @@ if (NOT USE_SYSTEM_MALLOC)
     list(APPEND WTF_LIBRARIES bmalloc)
 endif ()
 
+file(WRITE ${CMAKE_BINARY_DIR}/test_atomics.cpp
+     "int main(void)\n"
+     "{ long long x = 1; return (int) __sync_add_and_fetch_8(&x, 1); }\n")
+try_compile(ATOMICS_BUILD_SUCCEEDED ${CMAKE_BINARY_DIR} ${CMAKE_BINARY_DIR}/test_atomics.cpp)
+if (NOT ATOMICS_BUILD_SUCCEEDED)
+    list(APPEND WTF_SOURCES Atomics.cpp)
+endif ()
+file(REMOVE ${CMAKE_BINARY_DIR}/test_atomics.cpp)
+
 list(APPEND WTF_SOURCES
     unicode/icu/CollatorICU.cpp
 )