- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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

Factor out some common code from the libm tests. This is a bit messy
because different tests have different ideas about what it means to be
"close enough" to the right answer, depending on the properties of the
function being tested. In the process, I fixed some warnings and
added a few more 'volatile' hacks, which are sufficient to make all
the tests pass at -O2 with clang.

signbit() returns nonzero for negative arguments, but we shouldn't assume
that it always returns the same nonzero value.

Fix some warnings.

Add regression tests for fmin{,f,l} and fmax{,f,l}.
I wrote these to test amd64 asm functions that used
maxss, maxsd, minss, and minsd, but it turns out that
those instructions don't handle NaNs and signed zero
in the same way as fmin() and fmax() are required to,
so we're stuck with the C versions for now.