Add a triple to fix this test on Windows

The warning from cmake-clang-x64-msc16-R was:

  test\SemaCXX\old-style-cast.cpp Line 6: cast to 'void **' from smaller integer type 'long'

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195813 91177308-0d34-0410-b5e6-96231b3b80d8