Add USE_GCC_RUNTIME to x11/tk
Add USE_GCC_RUNTIME to chat/ejabberd
Add USE_GCC_RUNTIME to multimedia/ffmpeg010

This should not be necessary, but due to the way this package is
laid out, compiler.mk is read before USE_LIBTOOL is set, so we need
to add USE_GCC_RUNTIME early.  It should be possible to re-organise
the Makefile to avoid this completely.