BaseTools RVCT: ignore various RVC diagnostics

BaseTools RVCT: ignore various RVC diagnostics

This updates the RVCT CC flags so various diagnostics that trigger
warnings-as-errors are silenced. In particular, RVCT complains about
missing newlines at the end of source files, mixing of enums and int
values and return statements followed by a break, all of which occur
in the Tianocore codebase, but none of which are actual errors in the
code. So just silence them.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>