[libc] Fix couple of corner cases in remquo.

These two cases are fixed:

- If numerator is not zero and denominator is infinity, then the

numerator is returned as the remainder.

- If numerator and denominator are equal in magnitude, then quotient

with the right sign is returned.

The differet tests of remquo, remquof and remquol have been unified

into a single file to avoid duplication.

Reviewed By: lntue

Differential Revision: https://reviews.llvm.org/D92353