_STD -> _VSTD to avoid macro clash on windows

llvm-svn: 134190
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: ce48a1137d56d368828d360e5f2a8162bac6517c
diff --git a/src/iostream.cpp b/src/iostream.cpp
index b4b29c8..157c397 100644
--- a/src/iostream.cpp
+++ b/src/iostream.cpp
@@ -33,11 +33,11 @@
 ios_base::Init::Init()
 {
     cin.tie(&cout);
-    _STD::unitbuf(cerr);
+    _VSTD::unitbuf(cerr);
     cerr.tie(&cout);
 
     wcin.tie(&wcout);
-    _STD::unitbuf(wcerr);
+    _VSTD::unitbuf(wcerr);
     wcerr.tie(&wcout);
 }