Linux was complaining about ambiguous conditional expressions.
Added some explicit casts to RValue<Int> to fix these warnings.

Change-Id: Ib8e01ee69bb1794ea60b7954f1520a15e383cefa
Reviewed-on: https://swiftshader-review.googlesource.com/8111Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>