DirectAdmin and PHP 8+ leads to configure: error: iconv does not support errno

You might have an old iconv installed in /usr/local. It seems that DirectAdmin no longer manages its own libiconv, but the historic version in /usr/local can still get used by configure scripts that check /usr/local first.

The fix is to add a line to configure/php/configure.php83 (or the file for your PHP version):

--with-iconv=/usr/lib

Then try compilation again:

% ./build php_export 8.3 php-fpm