From the SPIR-V spec:
  OpSMod's result is the remainder r of Operand 1 divided by Operand 2
  where if r != 0, the sign of r is the same as the sign of Operand 2.

The less than comparison here was trying to correct the cases where C's
modulo had a different sign than SPIR-V's modulo. We can solve this by
directly comparing the sign of the C modulo against Operand 2's sign.

Bug chromium:973848

Change-Id: I27c88b7aaed35db5ba4df2cc0aac6061098f32c4
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/32868Tested-by: Sean Risser <srisser@google.com>
Presubmit-Ready: Sean Risser <srisser@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>