malloc/obstack: Merge from gnulib

Merge the latest version of the obstack.c and obstack.h files
from gnulib. The majority of this change is coding style and
cosmetic comment changes but it also fixes a -Wundef warning
in the build as a side effect.

2014-07-02  Will Newton  <will.newton@linaro.org>

	* malloc/obstack.c: Merge from gnulib master.
	[HAVE_CONFIG_H]: Remove conditional code.
	[!_LIBC]: Include config.h.
	[!ELIDE_CODE]: Don't include inttypes.h, include
	stdint.h unconditionally.
	(print_and_abort): Mark as _Noreturn.
	(_obstack_allocated_p): Mark as __attribute_pure__.
	(obstack_free): Rename to __obstack_free.
	[!__attribute__]: Remove conditional code.
	* malloc/obstack.h: Merge from gnulib master.
	[__cplusplus]: Move conditional down.
	[!__attribute_pure__]: Define __attribute_pure__ here
	if it is not already defined.
	(_obstack_memory_used): Mark as __attribute_pure__.
	[!__obstack_free]: Define as obstack_free.
	[__GNUC__]: Remove check for ancient NeXT gcc.