Reactor's 'Int' type is specified to be 32-bit, always, and it was
implicitly assumed the C++ 'int' type has the same size. Likewise for
'short' being 16-bit.

Make this assumption explicit with static asserts.

Bug: b/145913083
Change-Id: Ie47346358487f8152f68654b75ea44b5d4f8823b
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/39129
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>