clang-cl: Ignore the new /ZH options

These were added to the MS docs in
https://github.com/MicrosoftDocs/cpp-docs/commit/85b9b6967e58e485251450f7451673f6fc873e88
and are supposedly available in VS 2019 16.4 (though my 2019 Preview,
version 16.4.0-pre.1.0 don't seem to have them.)

llvm-svn: 373887