MMX on i386

[John Carr <jfc at tiac dot net>]

I started work on generating MMX instructions on i386.  I'm not likely
to find time in the near future to do more work.  So anyone who wants
to look at my incomplete changes can fetch

	http://www.mit.edu/~jfc/mmx.tar.gz

Basically, -mmmx (maybe this should be -mmx, imitating the mips
machine description's abuse of flag spelling) disables the floating
point coprocessor and adds 8 64 bit registers.

These changes are neither working nor complete.  There are some
experimental changes which probably make code worse.  If you use
floating point the compiler may crash or generate bad code.  You
probably don't want to look at these files unless you're a gcc hacker
and you like debugging the reload pass.