[compiler-rt] [builtins] Don't build __atomic_* by default.

Eli Friedman · Eli Friedman · commit 16c44560227c · 2018-06-14T23:22:53.000Z
The locks need to be implemented in a shared library to work correctly, so they shouldn't be part of libclang_rt.builtins.a, except in specialized scenarios where the user can prove it will only be linked once. Differential Revision: https://reviews.llvm.org/D47606 llvm-svn: 334779
diff --git a/compiler-rt/lib/builtins/CMakeLists.txt b/compiler-rt/lib/builtins/CMakeLists.txt
@@ -173,8 +173,8 @@ set(GENERIC_TF_SOURCES
   trunctfsf2.c)
 
 option(COMPILER_RT_EXCLUDE_ATOMIC_BUILTIN
-  "Skip the atomic builtin (this may be needed if system headers are unavailable)"
-  Off)
+  "Skip the atomic builtin (these should normally be provided by a shared library)"
+  On)
 
 if(NOT FUCHSIA AND NOT COMPILER_RT_BAREMETAL_BUILD)
   set(GENERIC_SOURCES
