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!

llvm-svn: 90748

llvm/include/llvm/System/Atomic.h

@@ -20,7 +20,11 @@ namespace llvm {
   namespace sys {
     void MemoryFence();
 
+#ifdef _MSC_VER
+    typedef long cas_flag;
+#else
     typedef uint32_t cas_flag;
+#endif
     cas_flag CompareAndSwap(volatile cas_flag* ptr,
                             cas_flag new_value,
                             cas_flag old_value);

llvm/lib/System/Atomic.cpp

@@ -85,7 +85,7 @@ sys::cas_flag sys::AtomicAdd(volatile sys::cas_flag* ptr, sys::cas_flag val) {
 #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