The clever pointer tricks were actually not working, and we were doing
the byte-by-byte moves in general.  By just doing the memcpy and
obvious byte swap code, we end up generating actual byte swap
instructions, thanks to optimizing compilers.

         text	   data	    bss	    dec	    hex	filename
before: 2240807	  51552	 132016	2424375	 24fe37	hw/xfree86/Xorg
after:  2215167	  51552	 132016	2398735	 249a0f	hw/xfree86/Xorg

Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Keith Packard <keithp@keithp.com>