64-bit obstack support

  In https://sourceware.org/ml/binutils/2014-07/msg00137.html, I bumped
OBSTACK_INTERFACE_VERSION, thinking that with an int -> size_t change
on some function parameters we obviously have an ABI change.

However, it seems that the bump is not really necessary due to the
following:

- the existing obstack support only works for obstacks sized up to
  INTMAX, so we only need to be compatible if passing a size_t in the
  positive int range.
- on 32-bit targets supported by glibc, sizeof(int) == sizeof(size_t),
  so for those targets the change is just substituting an unsigned
  parameter for one that was signed.
- on 64-bit targets supported by glibc, a size_t parameter (at least
  for the first or second parameter) or return from a function, is
  passed in the same register as an int.  I checked aarch64, alpha,
  mips64, powerpc64, s390x, sh64, sparc64, tilegx, x64_64.

That leaves non-glibc supported targets to consider, but I wonder if
they are worth worrying about..  I expect that most modern 64-bit
targets would prove to be similar in that int and size_t are passed to
functions in registers.

Note that in contrast to my previous patch, this one does not make
obstack.chunk_size a size_t, over concern that x86_64-mingw would see
an ABI change if I did that.

Comments?  (Maybe at the Cauldron, I'm about to catch a plane!)

	PR gdb/17133
	* malloc/obstack.h: Formatting.  Test HAVE_STRING_H.
	(__PTR_INT_TYPE): Rename from PTR_INT_TYPE.
	(__attribute_pure__): Define without reference to glibc macro.
	(__extension__): Avoid warning when __GNUC_MINOR__ undefined.
	(struct obstack): Make chunk_size unsigned long, and temp union
	with size_t.  Correct chunkfun prototype to take a size_t.
	(_obstack_newchunk): Update prototype.
	(_obstack_begin, _obstack_begin_1, _obstack_memory_used): Likewise.
	(__obstack_free): Define as _obstack_free.
	(obstack_init, obstack_begin, obstack_specify_allocation_with_arg,
	obstack_chunkfun): Update alloc function casts, formatting.
	For __STDC__ versions of the following macros:
	(obstack_object_size): Return size_t.
	(obstack_room): Likewise, and rename __o.
	(obstack_make_room): Make __len size_t, and use obstack_room.
	(obstack_grow, obstack_grow0, obstack_1grow, obstack_ptr_grow,
	obstack_int_grow, obstack_blank): Likewise.
	(obstack_finish): Use unsigned comparison when comparing aligned
	next_free against chunk_limit.
	(obstack_free): Cast OBJ to remove possible const qualifier.
	Don't wrap __obstack_free in parentheses.
	For !__STDC__ versions of the following macros:
	(obstack_object_size, obstack_room): Return size_t.
	(obstack_make_room): Use temp.i and obstack_room.
	(obstack_grow, obstack_grow0, obstack_1grow, obstack_ptr_grow,
	obstack_int_grow, obstack_blank): Likewise.
	(obstack_finish): Use temp.p.  Use unsigned comparision when
	comparing aligned next_free against chunk_limit.
	(obstack_free): Use temp.p and same comparisons as __STDC__ version.
	Don't wrap __obstack_free in parentheses.
	* malloc/obstack.c: Test HAVE_CONFIG_H.  Include gnu-versions.h.
	(COPYING_UNIT): Delete.
	(_Noreturn): Don't rely on this being defined, define ..
	(__attribute_noreturn__): ..and use this instead.
	(CALL_CHUNKFUN): Update chunkfun cast.
	(chunkfun_t, freefun_t): New typdefs.
	(_obstack_begin_worker): Split out from ..
	(_obstack_begin, _obstack_begin_1): ..here.  Make "size" param
	unsigned long, and correct chunkfun prototype.
	(_obstack_newchunk): Make "length" param size_t and local
	vars size_t.  Use memcpy to move existing object.
	(obstack_free): Update alias.
	(_obstack_memory_used): Return and use size_t local.

64-bit obstack support

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