In the autoreconf(1) man page:

       -i, --install
              copy missing auxiliary files

However, when AM_GNU_GETTEXT_VERSION is used, autoreconf runs
autopoint, which wants to override existing files, and fails
if existing files do not have the same contents as the autopoint
files:

autopoint: File ABOUT-NLS has been locally modified.
autopoint: File config.rpath has been locally modified.
autopoint: File m4/iconv.m4 has been locally modified.
autopoint: File po/Makefile.in.in has been locally modified.
autopoint: File po/Rules-quot has been locally modified.
autopoint: File po/en@boldquot.header has been locally modified.
autopoint: File po/en@quot.header has been locally modified.
autopoint: File po/insert-header.sin has been locally modified.
autopoint: File po/remove-potcdate.sin has been locally modified.
autopoint: *** Some files have been locally modified. Not overwriting them because --force has not been specified. For your convenience, you find the local modifications in the file '/tmp/arBTaNwR/gt73Yphm/autopoint.diff'.
autopoint: *** Stop.
autoreconf: autopoint failed with exit status: 1

This "error" should not be fatal for autoreconf.

As a workaround, in such a project (here, the current Mutt master),
it seems that AM_GNU_GETTEXT_VERSION may not be necessary. But if
AM_GNU_GETTEXT_VERSION is not used, autoreconf warns:

autoreconf: configure.ac: AM_GNU_GETTEXT is used, but not AM_GNU_GETTEXT_VERSION