Attempt to make MSVC happy.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@104432 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/ArgList.cpp b/lib/Driver/ArgList.cpp
index dbcc115..3d07431 100644
--- a/lib/Driver/ArgList.cpp
+++ b/lib/Driver/ArgList.cpp
@@ -118,7 +118,7 @@
 }
 
 int ArgList::getLastArgIntValue(OptSpecifier Id, int Default,
-                                Diagnostic &Diags) const {
+                                clang::Diagnostic &Diags) const {
   int Res = Default;
 
   if (Arg *A = getLastArg(Id)) {