Include gettext's m4 into the distribution.

@@ -11,4 +11,21 @@ EXTRA_DIST = \
  mu_libobj.m4 \
  realloc.m4 \
  regex.m4 \
- utmp.m4
+ utmp.m4 \
+ 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