bug#33166: automake --add-missing does not install config.rpath when AM_ICONV is used

[Bruno Haible]

> I need iconv but not gettext.

Then take the Gnulib module 'iconv'. [1][2] It contains iconv.m4, its
macro dependencies, and config.rpath - that is, exactly what you need.

Bruno

[1] https://www.gnu.org/software/gnulib/MODULES.html#module=iconv
[1] https://www.gnu.org/software/gnulib/manual/html_node/iconv.html