Patch 2/4 of the effort to make TLS access async-signal-safe.

Patch 2/4 of the effort to make TLS access async-signal-safe.
Add a signal-safe malloc replacement.

2013-12-18  Andrew Hunter  <ahh@google.com>

	* sysdeps/generic/ldsodefs.h (__signal_safe_memalign): New prototype.
	(__signal_safe_malloc, __signal_safe_free): Likewise.
	(__signal_safe_realloc, __signal_safe_calloc): Likewise.
	* elf/dl-misc.c (__signal_safe_allocator_header): New struct.
	(__signal_safe_memalign, __signal_safe_malloc): New function.
	(__signal_safe_free, __signal_safe_realloc): Likewise.
	(__signal_safe_calloc): Likewise.
	* elf/dl-tls.c (allocate_dtv, _dl_clear_dtv): Call signal-safe
	functions.
	(_dl_deallocate_tls, _dl_update_slotinfo): Likewise.