Fix bootstrap problem on Darwin.

[Geoffrey Keating]

This fixes the bootstrap problem that the regression tester is
reporting on rs6000-darwin.

Eventually this code can go away, because future Darwin versions won't
need it and existing Darwin versions already have the code in the
system libgcc; but there's still a possibility that I might need to
include a newer version of libgcc in a software update, so I'll leave
it in for a while.

Not tested at all, it can hardly make things worse...

===File ~/patches/rs6000-darwin-unwindfallbackcr2.patch=====
2007-07-15  Geoffrey Keating  <geoffk@apple.com>

	* config/rs6000/darwin-fallback.c (interpret_libc): Change
	CR2_REGNO to R_CR2.

Index: gcc/config/rs6000/darwin-fallback.c
===================================================================
--- gcc/config/rs6000/darwin-fallback.c	(revision 126659)
+++ gcc/config/rs6000/darwin-fallback.c	(working copy)
@@ -72,7 +72,7 @@
   gprs[1] = _Unwind_GetCFA (context);
   for (; i < 32; i++)
     gprs[i] = _Unwind_GetGR (context, i);
-  cr = _Unwind_GetGR (context, CR2_REGNO);
+  cr = _Unwind_GetGR (context, R_CR2);
 
   /* For each supported Libc, we have to track the code flow
      all the way back into the kernel.
============================================================