Fix -Wundef warnings for _ABI* on MIPS.

This patch fixes -Wundef warnings related to the _ABI* macros on MIPS.
GCC predefines only the _ABI* macro related to the ABI actually in
use, meaning that a conditional such as "#if _MIPS_SIM == _ABI64" is
true only for the ABI in question (all the macros are nonzero), but
produces a -Wundef warning for the other ABIs.  The normal approach to
using these macros is to include <sgidefs.h>, which ensures that all
three _ABI* macros are defined rather than just one; this patch does
so in the places that caused warnings (the bulk of the warnings
arising from <bits/wordsize.h>).  Tested that the warnings are fixed.

	* sysdeps/mips/bits/wordsize.h: Include <sgidefs.h>.
	* sysdeps/unix/sysv/linux/mips/getrlimit64.c: Likewise.
	* sysdeps/unix/sysv/linux/mips/setrlimit64.c: Likewise.

ChangeLog

@@ -1,5 +1,9 @@
 2014-03-21  Joseph Myers  <joseph@codesourcery.com>
 
+	* sysdeps/mips/bits/wordsize.h: Include <sgidefs.h>.
+	* sysdeps/unix/sysv/linux/mips/getrlimit64.c: Likewise.
+	* sysdeps/unix/sysv/linux/mips/setrlimit64.c: Likewise.
+
 	[BZ #16731]
 	* sysdeps/i386/fpu/e_log.S (__ieee754_log): Take absolute value
 	when x - 1 is zero.

sysdeps/mips/bits/wordsize.h

@@ -15,6 +15,8 @@
    License along with the GNU C Library.  If not, see
    <http://www.gnu.org/licenses/>.  */
 
+#include <sgidefs.h>
+
 #define __WORDSIZE	_MIPS_SZPTR
 #if _MIPS_SIM == _ABI64
 # define __WORDSIZE_TIME64_COMPAT32	1

sysdeps/unix/sysv/linux/mips/getrlimit64.c

@@ -15,6 +15,8 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#include <sgidefs.h>
+
 #if _MIPS_SIM == _ABIO32 || _MIPS_SIM == _ABIN32
 
 # include <shlib-compat.h>

sysdeps/unix/sysv/linux/mips/setrlimit64.c

@@ -15,6 +15,7 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#include <sgidefs.h>
 
 #if _MIPS_SIM == _ABIO32 || _MIPS_SIM == _ABIN32