There were only a handful of integer conversion warnings in
libGLESv2, so I fixed them rather than silencing them.

Change-Id: I94a7f2d4e4c34a48a8f128e6303778ef23ac45c9
Reviewed-on: https://swiftshader-review.googlesource.com/7132Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>