patch applied (ghc): A better x86_64 register mapping, with more argument registers.

[Simon Marlow]

Tue Feb 28 07:36:40 PST 2006  Simon Marlow <simonmar at microsoft.com>
  * A better x86_64 register mapping, with more argument registers.
  
  Now that we can handle using C argument registers as global registers,
  extend the x86_64 register mapping.  We now have 5 integer argument
  registers, 4 float, and 2 double (all caller-saves).  This results in a
  reasonable speedup on x86_64.

    M ./ghc/includes/MachRegs.h -32 +31
    M ./ghc/rts/StgCRun.c -2 +2