Fix reference to toc symbol.

https://sourceware.org/ml/binutils/2014-03/msg00033.html removes the
"magic" treatment of symbols defined in a .toc section.

	* sysdeps/powerpc/powerpc64/start.S: Add @toc to toc symbol reference.
Correct prefetch hint in power7 memrchr.

Typo fix.

	* sysdeps/powerpc/powerpc64/power7/memrchr.S: Correct stream hint.
Correct IBM long double nextafterl.

Fix for values near a power of two, and some tidies.

	[BZ #16739]
	* sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c (__nextafterl): Correct
	output when value is near a power of two.  Use int64_t for lx and
	remove casts.  Use decimal rather than hex exponent constants.
	Don't use long double multiplication when double will suffice.
	* math/libm-test.inc (nextafter_test_data): Add tests.
	* NEWS: Add 16739 and 16786 to bug list.