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.

As detailed in PR11157, the use of '__block' is known to interfere
with keywords in some environments, such as the Clang -fblocks extension.
Recently a similar issue was raised concerning the use of '__unused'
and a '__glibc' prefix was proposed to create a glibc implementation
namespace for these sorts of issues [1].  This patches takes that
approach.

[1] https://sourceware.org/ml/libc-alpha/2012-02/msg00047.html
[2] http://lists.debian.org/debian-glibc/2013/11/msg00020.html