Support for Thread Safety Analysis in C

Patch by Ethan Jackson.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187365 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Lex/PPMacroExpansion.cpp b/lib/Lex/PPMacroExpansion.cpp
index 899fba6..a9d76c3 100644
--- a/lib/Lex/PPMacroExpansion.cpp
+++ b/lib/Lex/PPMacroExpansion.cpp
@@ -902,6 +902,7 @@
            .Case("attribute_unavailable_with_message", true)
            .Case("attribute_unused_on_fields", true)
            .Case("blocks", LangOpts.Blocks)
+           .Case("c_thread_safety_attributes", true)
            .Case("cxx_exceptions", LangOpts.Exceptions)
            .Case("cxx_rtti", LangOpts.RTTI)
            .Case("enumerator_attributes", true)