[configure PATCH] Do not rerun fixincludes during toplevel bootstrap

[Paolo Bonzini]

> Specs shouldn't vary from stage to stage, but they might, I suppose.  :-/

They don't -- the gcc Makefile has special stuff in it to build the 
specs just once:

   # fixinc.sh depends on this, not on specs directly.
   # The idea is to make sure specs gets built, but not rerun fixinc.sh
   # after each stage just because specs' mtime has changed.
   specs.ready: specs
	  -if [ -f specs.ready ] ; then \
		  true; \
	  else \
		  $(STAMP) specs.ready; \
	  fi

I figured that toplevel bootstrap would rebuild the specs every time, 
but fixincludes would not be run.

Todo list for toplevel bootstrap:
- add bootstrap-lean targets (can do this soon)
- test combined tree
- test parallel makes
- ask people to use it
- fix bugs :-)
- enable it definitely
- remove cruft from gcc and toplevel Makefile

Paolo