Disabled a few warnings and fixed a few warnings to enable
turning 'warnings as errors' on in Visual Studio.

Change-Id: I91e8e2d4d71794b73178f8d59c2f6fc872ad3085
Reviewed-on: https://swiftshader-review.googlesource.com/5710Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>