Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Replace use of ${.CURDIR} by ${LIBC_SRCTOP} and define ${LIBC_SRCTOP}
if not already defined. This allows building libc from outside of
lib/libc using a reach-over makefile.

A typical use-case is to build a standard ILP32 version and a COMPAT32
version in a single iteration by building the COMPAT32 version using a
reach-over makefile.

Obtained from: Juniper Networks, Inc.

libc_r wasn't so tied to libc for 22 months.

We typically don't add trailing /'s.

Add code to emulate arithmetic, comparison and conversion operations
on long double, which are not implemented in hardware on any UltraSPARC
chip that I know of. This just calls into the existing floating point
emulator, which is still needed to emulate other floating point operations
in certain conditions. Without this gcc has to generate the quad floating
point instructions directly, which sometimes causes internal compiler
errors.

Reviewed by: tmm

Emulate ldq and stq (load/store long double) instructions. GCC has started
using these to load long doubles, but they aren't implemented in hardware
on (at least) UltraSPARC I and II machines.
Emulate popc in the user trap handler as well.
Re-arrange slightly to make support functions more accessible.

Reviewed by: tmm

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.