Subzero emits incorrect code for FRem operations on vectors. Replace
with an emulated version that calls fmodf on each component for now.

Bug: b/148139679
Change-Id: Ib541370b71b99649f8c73f982fd12cb3cde25e7f
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/40450
Presubmit-Ready: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>