Fix -Wundef warnings.  Upstream addressed this as part of this commit:

commit b100f9aa77027e4371154820ea8a0353bfd13223

Author: Will Newton <will.newton@linaro.org>

Date:   Mon Jun 23 16:53:30 2014 +0100

    malloc/obstack: Merge from gnulib

diff --git a/malloc/obstack.c b/malloc/obstack.c

index e3ce53f987727eca..2b103727e010b417 100644

--- a/malloc/obstack.c

+++ b/malloc/obstack.c

@@ -56,10 +56,10 @@

 #ifndef ELIDE_CODE

-# if HAVE_INTTYPES_H

+# if _LIBC || HAVE_INTTYPES_H

 #  include <inttypes.h>

 # endif

-# if HAVE_STDINT_H || defined _LIBC

+# if _LIBC || HAVE_STDINT_H

 #  include <stdint.h>

 # endif

diff --git a/malloc/obstack.h b/malloc/obstack.h

index a791823cf3f18348..69e92d1146b02eb1 100644

--- a/malloc/obstack.h

+++ b/malloc/obstack.h

@@ -250,13 +250,6 @@ extern int obstack_exit_failure;

 #define obstack_memory_used(h) _obstack_memory_used (h)

 #if defined __GNUC__

-/* NextStep 2.0 cc is really gcc 1.93 but it defines __GNUC__ = 2 and

-   does not implement __extension__.  But that compiler doesn't define

-   __GNUC_MINOR__.  */

-# if __GNUC__ < 2 || (__NeXT__ && !__GNUC_MINOR__)

-#  define __extension__

-# endif

-

 /* For GNU C, if not -traditional,

    we can define these macros to compute all args only once

    without using a global variable.