Ignore gettext's m4 files.

 Makefile
 Makefile.in
+iconv.m4
+codeset.m4
+gettext.m4
+glibc21.m4
+intdiv0.m4
+inttypes-pri.m4
+inttypes.m4
+inttypes_h.m4
+isc-posix.m4
+lcmessage.m4
+lib-ld.m4
+lib-link.m4
+lib-prefix.m4
+progtest.m4
+stdint_h.m4
+uintmax_t.m4
+ulonglong.m4