Faster compilation speed

[David S. Miller]

   From: Dale Johannesen <dalej@apple.com>
   Date: Wed, 14 Aug 2002 10:17:46 -0700
   
   And I know this is blindingly obvious, but RC takes an extra field (word,
   probably) in each node.  I suspect this is going to eat up a lot of
   whatever gain there might be.
   
My implementation (I posted the hacked up infrastructure patch the
other day) used space which is currently empty alongside a bitfield
in the rtx.