Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Let PowerPC world optionally build with -msoft-float. For FPU-less PowerPC
variations (e500 currently), this provides a gcc-level FPU emulation and is an
alternative approach to the recently introduced kernel-level emulation
(FPU_EMU).

Approved by: cognet (mentor)
MFp4: e500

Use C comments since we now preprocess these files with CPP.

Add symbol versioning to libm.

Replace fegetmask() and fesetmask() with feenableexcept(),
fedisableexcept(), and fegetexcept(). These two sets of routines
provide the same functionality. I implemented the former as an
undocumented internal interface to make the regression test easier to
write. However, fe(enable|disable|get)except() is already part of
glibc, and I would like to avoid gratuitous differences. The only
major flaw in the glibc API is that there's no good way to report
errors on processors that don't support all the unmasked exceptions.

Define the LDBL_PREC to be the number of significant bits in a long
double's mantissa.

Mark all inline asms that read the floating-point control or status
registers as volatile. Instructions that *wrote* to FP state were
already marked volatile, but apparently gcc has license to move
non-volatile asms past volatile asms. This broke amd64's feupdateenv
at -O2 due to a WAR conflict between fnstsw and fldenv there.

Add an fenv.h implementation for the powerpc port.

Reviewed by: standards@