[PATCH][Revised] fix --enable-build-with-cxx on darwin

[Jack Howarth]

Currently the bootstrap with --enable-build-with-cxx is broken due to compiler 
errors of the form
"error: converting 'false' to pointer type 'varpool_node*' 
[-Werror=conversion-null]". The attached
patch changes the last remaing instance of false to NULL and restores the 
--enable-build-with-cxx bootstrap.
Tested on x86_64-apple-darwin10. Okay for gcc trunk?
                Jack

2011-05-05  Jack Howarth <howa...@bromo.med.uc.edu>

        * gcc/varpool.c (varpool_extra_name_alias): Likewise.

Index: gcc/varpool.c
===================================================================
--- gcc/varpool.c       (revision 173423)
+++ gcc/varpool.c       (working copy)
@@ -676,7 +676,7 @@ varpool_extra_name_alias (tree alias, tr
 
 #ifndef ASM_OUTPUT_DEF
   /* If aliases aren't supported by the assembler, fail.  */
-  return false;
+  return NULL;
 #endif
 
   gcc_assert (TREE_CODE (decl) == VAR_DECL);