libiberty patch - configure/makefile for cygwin

[Jeffrey A Law]

  In message < 200008042044.QAA20304@envy.delorie.com >you write:
  > > So ultimately, after Alexandre's recent hackery, what is the right
  > > thing to do to get cygwin builds working again independently of gcc?
  > 
  > This patch should mean "if we're also building gcc, and it's a gcc
  > that will run on the build machine, we want to use its includes
  > instead of the system's default includes".  Right?
Yes.

  > Otherwise, the target libiberty's Makefile now includes -I's for
  > newlib, so that's fixed.
OK.  

jeff