a) Don't be concerned about "not polluting the namespace with stddef.h
symbols" in obstack.h, since gnulib string.h includes stddef.h
anyway, and it seems unlikely that anyone would care.
b) Don't roll our own slow memcpy in _obstack_newchunk.
c) Rename obstack_free to _obstack_free. This makes the naming
consistent with other obstack functions and obviates the need for
__obstack_free. Ancient obstack.c defined both obstack_free and
_obstack_free. We continue to do that for _LIBC via an alias.
d) Miscellaneous macro fixes. The expression used to test for gcc-2.8
is clever, but nowadays gcc warns on undefined macros. You'll get
an undefined macro warning if simulating an old gcc with -U__GNUC__
-U__GNUC_MINOR__ -D__GNUC__=1.
* lib/obstack.h: Include stddef.h unconditionally. Formatting fixes.
(PTR_INT_TYPE): Delete, replace with ptrdiff_t.
(__obstack_free): Delete, update refs.
(_obstack_free): Rename from obstack_free.
(__extension__): Avoid undefined macro warning for __GNUC_MINOR__.
(obstack_object_size, obstack_room): Parenthesise !__GNUC__ versions.
* lib/obstack.c: Don't include stddef.h.
(COPYING_UNIT): Delete.
(_obstack_begin): Formatting fix.
(_obstack_newchunk): Use memcpy to move existing object to new chunk.
(_obstack_free): Rename from __obstack_free, update alias. Move
undef of obstack_free to where it is needed.