Conversion from floating-point to unsigned integer is not a native
instruction on some CPU architectures, so excercise the case where it
overflows signed int.

Bug: b/31816482
Change-Id: I4ce924bbf4eb4c371e25d800fd4d7794edfa62cb
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/39188
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>