MFC r317845-r317846

MFC r317845-r317846

r317845:
Provide a freebsd32 implementation of sigqueue()

The previous misuse of sys_sigqueue() was sending random register or
stack garbage to 64-bit targets.  The freebsd32 implementation preserves
the sival_int member of value when signaling a 64-bit process.

Document the mixed ABI implementation of union sigval and the
incompability of sival_ptr with pointer integrity schemes.

Reviewed by:	kib, wblock
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D10605

r317846:
Regen post r317845.

MFC with:	r317845
Sponsored by:	DARPA, AFRL

git-svn-id: svn://svn.freebsd.org/base/stable/10@318323 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f