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

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

Use __FBSDID

Add userland floating point emulator code for sparc64. This is a port
of the (never committed) in-kernel version (with some optimizations and
cleanups), which in turn was ported from NetBSD.