Reactor: Fix Round (float) generic code generation

Reactor: Fix Round (float) generic code generation

This commit fixes `Round(Float)` and `Round(Float4)` generic LLVM code
generation.

Bug: b/115344057
Test: dEQP-GLES3.functional.shaders.builtin_functions.precision.sin
Test: dEQP-GLES3.functional.shaders.builtin_functions.precision.cos
Change-Id: I9758ac4ca69bb0f5a5b192b4be3310827625fac0
Reviewed-on: https://swiftshader-review.googlesource.com/20932
Tested-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>