devel/gettext-runtime: Fix crash triggered by libgpg-error

Libgpg-error has an initialisation function with
attribute((constructor)) that calls a libintl function that
calls pthread_rwlock_wrlock that segfaults if libpthread wasn't
initialised yet. This can happen because libintl doesn't link to
libpthread to avoid the overhead for non-threaded programs. To
fix this, add an initialisation function to libintl that triggers
initialisation of libpthread.

RTLD_NOLOAD suggested by kib.

dlopen was fixed to work during initialisation in
https://cgit.FreeBSD.org/src/commit/?id=1005d3d05362

PR: 272472, 272517