[patch ada]: Fix bootstrap for Ada

[Kai Tietz]

Hi,

this patch fixes an obvious bootstrap issue caused by trying to assign
a constant pointer to an none-constant.

Index: adaint.c
===================================================================
--- adaint.c    (revision 174060)
+++ adaint.c    (working copy)
@@ -3367,8 +3367,8 @@
 char *
 __gnat_to_canonical_file_list_next (void)
 {
-  static char *empty = "";
-  return empty;
+  static char empty[1];
+  return &empty[0];
 }

 void