Fix the build on Cygwin.  Patch by Aaron Gray.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74510 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/Annotation.cpp b/lib/Support/Annotation.cpp
index b778043..4b5b97e 100644
--- a/lib/Support/Annotation.cpp
+++ b/lib/Support/Annotation.cpp
@@ -39,7 +39,7 @@
 }
 
 typedef std::map<const char*, unsigned, StrCmp> IDMapType;
-static unsigned IDCounter = 0;  // Unique ID counter
+static volatile sys::cas_flag IDCounter = 0;  // Unique ID counter
 
 // Static member to ensure initialiation on demand.
 static ManagedStatic<IDMapType> IDMap;