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

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
index 5e7f224..99184ba 100644 (file)
--- 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