Bug: b/126873455
Tests: dEQP-VK.glsl.builtin.function.common.modf.*

Change-Id: Icefc1f7241aa1b3ef253b9f5775c38a424afec77
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/28569
Presubmit-Ready: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Ben Clayton <bclayton@google.com>