clang/test/SemaCXX/ms-iunknown-template-function.cpp: Appease for targeting *-win32.

This expects the warning;

  File clang/test/SemaCXX/ms-iunknown-template-function.cpp Line 19: __declspec attribute 'novtable' is not supported

But for targeting *-win32, the warning is not seen.

  error: 'warning' diagnostics expected but not seen:
    File clang\test\SemaCXX\ms-iunknown-template-function.cpp Line 19 (directive at clang\test\SemaCXX\ms-iunknown-template-function.cpp:18): __declspec attribute 'novtable'

llvm-svn: 314586