Fixes the Atomic implementation if compiled by MSVC compiler.

sys::cas_flag should be long on this platform, InterlockedAdd() is
defined only for the Itanium architecture (according to MSDN).

Patch by Michael Beck!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90748 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/System/Atomic.cpp b/lib/System/Atomic.cpp
index f9b55a1..7ba8b77 100644
--- a/lib/System/Atomic.cpp
+++ b/lib/System/Atomic.cpp
@@ -85,7 +85,7 @@
 #elif defined(__GNUC__)
   return __sync_add_and_fetch(ptr, val);
 #elif defined(_MSC_VER)
-  return InterlockedAdd(ptr, val);
+  return InterlockedExchangeAdd(ptr, val) + val;
 #else
 #  error No atomic add implementation for your platform!
 #endif