Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

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

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

These tests check whether the compiler evaluates floating-point
expressions properly. Some of the tests depend on the compiler
implementing C99's FENV_ACCESS pragma, and only commercial compilers
do; those tests are currently skipped. If any of the enabled tests
fail, then odds are the libm regression tests will fail also.
This should make it easier to diagnose reported problems on platforms
I don't have.

Currently, gcc passes all the tests that don't depend on FENV_ACCESS
on amd64 and sparc64. Clang fails a few on amd64 (see clang bug
11406). Both gcc and clang fare poorly on i386, which has well-known
issues.