In the past, gettext installed m4 files from gnulib.
By this commit in 2018:
https://git.savannah.gnu.org/gitweb/?p=gettext.git;a=commit;h=198164be9e4ebc706ad7ffcc0f8b6a0608ea3de9
It was changed no install of those m4 files.
extern-inline.m4 which was used by gnupg1 is affected.
We should include this.