Remove redundant nested function b64_from_24bit

Move multiple definitions of the nested function b64_from_24bit into a
single function __b64_from_24bit.
[AArch64] Cleanup declarations in math_private.h.
[AArch64] Switch from FE_TOWARDZERO to _FPU_FPCR_RM_MASK
[AArch64] Regenerate libm-test-ulps
aarch64: Consolidate NPTL/non versions of clone

At the same time, rely on non-clobbered registers across syscall
so that we eliminate the stack frame that we previously ignored
in the unwind info.
aarch64: Consolidate NPTL/non versions of vfork

At the same time, incorporate the 0 -> 0x80000000 mapping
of the pid expected by raise.c.
S/390: Regenerate ULPs.
aarch64: Remove nptl/vfork.S
Fix invalid file descriptor reuse while sending DNS query (BZ #15946)
Fixed pthread_spin_lock on sparc32/64 (bug 16882)

	[BZ #16882]
	* nptl/sysdeps/sparc/sparc32/pthread_spin_lock.S
	(pthread_spin_lock): Branch out of spin loop to proper location.
	* nptl/sysdeps/sparc/sparc64/pthread_spin_lock.S
	(pthread_spin_lock): Likewise.
New test for pthread_spin_lock (bug 16882)

	* nptl/tst-spin4.c: New test.
	* nptl/Makefile (tests): Add tst-spin4.
Fixup ChangeLog and add missing NEWS entry for previous commits.