Clean up <machine/ieeefp.h> and make sure the rounding mode bits match the

Clean up <machine/ieeefp.h> and make sure the rounding mode bits match the
hardware.  Implement fp[gs]etround(3) and fp[gs]etsticky(3) and tweak
the fp[gs]etmask(3) implementation to provide the right weak symbols.
This implementation deliberately ignores the additional
"round to nearest, away from zero" as this interface is derived from
i386-specific code and the i387 FPU doesn't implement such a rounding
mode.  This is a legacy API and code should use <fenv.h> instead.

ok drahn@