MFC r259525, r259526, r259529

MFC	r259525, r259526, r259529

gcc: small merges from upstream

fix ICE in rs6000 when using -fno-trapping-math.
Solves GCC-PR target/30485

Solve GCC issues:
PR middle-end/32602
PR middle-end/32603

Updates the to documentation and processing improvement.

Obtained from:	gcc 4.3 (rev. 120902, 120902, 119427, 126278, 126422;
		GPLv2)

git-svn-id: svn://svn.freebsd.org/base/stable/10@260139 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f