math: Order signed zeros in f{max,min}{f,l,f128}

math: Order signed zeros in f{max,min}{f,l,f128}

The C standard (at least from C99 until C23) does not require
fmin/fmax to order zeros by their sign, so glibc's previous behavior
was entirely standards-conforming.  However, the standard does
recommend that zeros be ordered in a footnote, saying:

"If possible, fmax is sensitive to the sign of zero, for example
fmax(−0.0, +0.0) ideally returns +0."

As this is indeed possible (and not too complicated), implement it as
a quality-of-implementation improvement.  It also remove possible
deviations between architectures, where for some architectures that
has direct mapping instruction (USE_FMA*_BUILTIN) they already do
the ordering.

Checked on x86_64-linux-gnu, aarch64-linux-gnu, i686-linux-gnu,
arm-linux-gnueabihf, powerpc64le-linux-gnu,
riscv64-linux-gnu-rv64imafdc-lp64d, and loongarch64-linux-gnuf64.

Co-authored-by: James Y Knight <jyknight@google.com>
Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>