regex: don't deref NULL upon heap allocation failure

* posix/regcomp.c: (parse_dup_op): Handle duplicate_tree
failure in one more place.
To trigger the segfault, configure grep -with-included-regex,
build it, and run these commands:
( ulimit -v 300000; echo a|src/grep -E a+++++++++++++++++++++ )
ChangeLog fix
Correct DT_PPC64_NUM

	[BZ #17153]
	* elf/elf.h (DT_PPC64_NUM): Correct value.
	* NEWS: Add to fixed bug list.
Enable AVX2 optimized memset only if -mavx2 works

	* config.h.in (HAVE_AVX2_SUPPORT): New #undef.
	* sysdeps/i386/configure.ac: Set HAVE_AVX2_SUPPORT and
	config-cflags-avx2.
	* sysdeps/x86_64/configure.ac: Likewise.
	* sysdeps/i386/configure: Regenerated.
	* sysdeps/x86_64/configure: Likewise.
	* sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Add
	memset-avx2 only if config-cflags-avx2 is yes.
	* sysdeps/x86_64/multiarch/ifunc-impl-list.c (__libc_ifunc_impl_list):
	Tests for memset_chk and memset only if HAVE_AVX2_SUPPORT is
	defined.
	* sysdeps/x86_64/multiarch/memset.S: Define multiple versions
	only if HAVE_AVX2_SUPPORT is defined.
	* sysdeps/x86_64/multiarch/memset_chk.S: Likewise.