Revised patch for insn elision

[David Edelsohn]

>>>>> Mark Mitchell writes:

Mark> David, if you don't feel like making this change Zack or I will take
Mark> care of it.

	Thanks.  I'm still debugging this.  Making that change allowed the
bootstrap to progress farther, but then ICEd later.  I then found that
both the common_init and common_expand parts were not protected by macros
after Aldy's SPE patch.  I am trying bootstrap again with

if (TARGET_ALTIVEC || TARGET_SPE)

wrapping those cases.  I think that I need both.

David