This CL removes some warning spam on a gcc build.

Bug chromium:697528
R=capn@google.com

Change-Id: I6909d30e3fcafc8ab7e3a98efe8d180a686781d8
Reviewed-on: https://swiftshader-review.googlesource.com/9031Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Tom Anderson <thomasanderson@google.com>