Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Fix a bug in remquo{,f,l}, in which the quotient didn't always have the
correct sign when the remainder was 0.

Fix a separate bug in remquo alone, in which the remainder and
quotient were both off by a bit in certain cases involving subnormal
remainders.

The bugs affected all platforms except amd64 and i386, on which the
routines are implemented in assembly.

PR: 166463
Submitted by: Ilya Burylov
MFC after: 2 weeks

Implement remquol() based on remquo().

Implement and document remquo() and remquof().