- Moving -Wall from the individual Makefiles to configure (and only

have it passed to GCC)
- Moving the usage in configure to the top of it, so you don't have to
wait needlessly
- Silence compiler output during configuration
- Add support for configuring with IBM XLC

patch by (Dan Christiansen <danchr at daimi dot au dot dk>)

Originally committed as revision 2397 to svn://svn.ffmpeg.org/ffmpeg/trunk