Provide an alias to _obstack_free

GDB 7.11 does not build if compiled against uclibc-ng (1.0.12 was used,
but the problematic code exists in 1.0.13 as well). The reason is that
GDB release includes its own obstack implementation, but elides the code
if <gnu-versions.h> declares a compatible obstack implementation in
libc. uclibc-ng does claim compatible obstack interface (GDB expects
version 2, but accepts version 1 if sizeof(int) == sizeof(size_t)),
however, uclibc-ng does not provide the _obstack_free symbol that is a
part of the interface (glibc does provide this symbol). This later
causes a link failure.

The attached patch makes uclibc-ng enables an alias _obstack_free ->
obstack_free.

Signed-off-by: Alexey Neyman <stilor@att.net>

libc/misc/gnu/obstack.c

@@ -385,11 +385,9 @@ obstack_free (struct obstack *h, void *obj)
     abort ();
 }
 
-# if 0
 /* Older versions of libc used a function _obstack_free intended to be
    called by non-GCC compilers.  */
 strong_alias (obstack_free, _obstack_free)
-# endif
 
 int
 _obstack_memory_used (struct obstack *h)