*  configure.in: Use AC_PREREQ(2.12.1).

From-SVN: r23802
diff --git a/libobjc/configure.in b/libobjc/configure.in
index d5cdc6a..f3c7c5b1 100644
--- a/libobjc/configure.in
+++ b/libobjc/configure.in
@@ -19,6 +19,7 @@
 #the Free Software Foundation, 59 Temple Place - Suite 330, Boston, MA
 #02111-1307, USA.
 
+AC_PREREQ(2.12.1)
 AC_INIT(objc/objc.h)
 #AC_CONFIG_HEADER(config.h)