https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93602
--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> --- Ah, something did change: we now use automake-1.15.1 and autoconf-2.69 and that's where all the iconv handling comes from (via the AM_ICONV macro). Presumably that changed in upstream automake.
