_STD -> _VSTD to avoid macro clash on windows

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@134190 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/exception b/include/exception
index 00fc6b8..f418575 100644
--- a/include/exception
+++ b/include/exception
@@ -199,7 +199,7 @@
 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
 {
 #ifndef _LIBCPP_NO_EXCEPTIONS
-    throw __nested<typename remove_reference<_Tp>::type>(_STD::forward<_Tp>(__t));
+    throw __nested<typename remove_reference<_Tp>::type>(_VSTD::forward<_Tp>(__t));
 #endif
 }
 
@@ -218,7 +218,7 @@
 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
 {
 #ifndef _LIBCPP_NO_EXCEPTIONS
-    throw _STD::forward<_Tp>(__t);
+    throw _VSTD::forward<_Tp>(__t);
 #endif
 }