Effectively revert r182453 - atomic.c may not be compiled if host compiler doesn't understand _Atomic

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@182478 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index 4e826e4..f07ab1e 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -37,7 +37,8 @@
   ashlti3.c
   ashrdi3.c
   ashrti3.c
-  atomic.c
+  # FIXME: atomic.c may only be compiled if host compiler understands _Atomic
+  # atomic.c
   clear_cache.c
   clzdi2.c
   clzsi2.c