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

Per Regents of the University of Calfornia letter, remove advertising
clause.

# If I've done so improperly on a file, please let me know.

Rewrite longjmp() and _longjmp() to directly restore the saved frame,
instead of unwinding the call stack. This makes them usable to switch
stacks, e.g. for libc_r.
Do not save the frame pointer in setjmp() and _setjmp(), it is not needed
any more.
Rename _longjmp() to ___longjmp(), with a weak alias to _longjmp(), like
the other architectures did.

Use __FBSDID.

Add .register directives for gcc3.
Adapt to jmpbuf no longer being a ucontext_t.
Call abort if longjmperror returns.

Catch up to jmpbuf changes. Define offsets used from assmebly language
in another file so that it is easy to see what they are and keep them in
sync with the headers (grafted from the kernel generated assym.s).

Minimal libc for sparc64.

Reviewed by: obrien