clang/test/CodeGenCXX/static-data-member-single-emission.cpp: Tweak for MS mangler.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@234687 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGenCXX/static-data-member-single-emission.cpp

@@ -4,6 +4,7 @@ template <typename T>
 struct HasStaticInit {
 static const int index;
 };
+extern "C"
 int the_count = 0;
 template <typename T>
 const int HasStaticInit<T>::index = the_count++;