Subzero does not support Bools as return types.
We were getting away with this as Return() was silently converting this to an Int.

Just use an Int as the return type.

Bug: b/131914569
Change-Id: I3bff7304b219f66cee7605ddd3cf6a1a75a8612a
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/30457Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Ben Clayton <bclayton@google.com>