SpirvShader: Fix for integer overflow in SDiv and SMod.

SpirvShader: Fix for integer overflow in SDiv and SMod.

See b/128614198 for context.

Tests: dEQP-VK.glsl.operator.binary_operator.div.*ivec*
Tests: dEQP-VK.glsl.operator.binary_operator.mod.*ivec*
Bug: b/128614198
Change-Id: I3c517a18ce003466b1ba382f1896b356e543f5d5
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/27248
Presubmit-Ready: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>