Disable clang -Wsigned-enum-bitfield warnings

Full error text:
error: enums in the Microsoft ABI are signed integers by default;
consider giving the enum Properties an unsigned underlying type
to make this code portable [-Werror,-Wsigned-enum-bitfield]

BUG=skia:

Change-Id: I1491dd94c894e383fed401880fc04562140f7a66
Reviewed-on: https://skia-review.googlesource.com/6594
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Matt Sarett <msarett@google.com>
1 file changed