PowerPC: Fix little endian enconding for mfvsrd

This patch fixes the MFVSRD_R3_V1 macro that encodes 'mfvsrd  r3,vs1'
(to support old binutils) for little endian.

Backport of 757d9dd5c3efa56fac75965abc014faaae7b7895.
Fix s_copysign stack temp for PowerPC64 ELFv2

	[BZ #16786]
	* sysdeps/powerpc/powerpc64/fpu/s_copysign.S: Don't trash stack.

Backport of c859b32e9d76afe8a3f20bb9528961a573c06937.
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.

Backport of 483818d768ed99a5edf4114298a75ebedaee8d5c.
Correct prefetch hint in power7 memrchr.

Typo fix.

	* sysdeps/powerpc/powerpc64/power7/memrchr.S: Correct stream hint.

Backport of af6b17973cbc07ac06cfb40eeab5cc2391fb489a.
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.

Backport of b0abbc21034f0e5edc49023d8fda0616173faf17.
PowerPC: Fix nearbyint/nearbyintf result for FE_DOWNWARD

This patch fixes the powerpc32 optimized nearbyint/nearbyintf bogus
results for FE_DOWNWARD rounding mode.  This is due wrong instructions
sequence used in the rounding calculation (two subtractions instead of
adition and a subtraction).

Fixes BZ#16815.

Backport of 8bd70862e11023e7f827f240a5a214f847ae982d.