Don't PROVIDE over top of common symbols

This:
  int end[100000];
  int main(void) { end[99999] = 0; return 0; }
should not segfault.

ld/
	* ldexp.c (exp_fold_tree_1 <etree_provide>): Leave bfd_link_hash_common
	symbols alone.
ld/testsuite/
	* ld-elf/endsym.s, *ld-elf/endsym.d: New test.

ld/ChangeLog

@@ -1,3 +1,8 @@
+2014-12-23  Alan Modra  <amodra@gmail.com>
+
+	* ldexp.c (exp_fold_tree_1 <etree_provide>): Leave bfd_link_hash_common
+	symbols alone.
+
 2014-12-23  Alan Modra  <amodra@gmail.com>
 
 	* ldexp.c (update_definedness): Correct logic setting by_object.

ld/ldexp.c

@@ -1070,15 +1070,15 @@ exp_fold_tree_1 (etree_type *tree)
 	      h = bfd_link_hash_lookup (link_info.hash, tree->assign.dst,
 					FALSE, FALSE, TRUE);
 	      if (h == NULL
-		  || (h->type != bfd_link_hash_new
+		  || !(h->type == bfd_link_hash_new
-		      && h->type != bfd_link_hash_undefined
+		       || h->type == bfd_link_hash_undefined
-		      && h->type != bfd_link_hash_common
+		       || (h->type == bfd_link_hash_defined
-		      && !(h->type == bfd_link_hash_defined
 			   && (h->u.def.section->flags
 			       & SEC_LINKER_CREATED) != 0)))
 		{
-		  /* Do nothing.  The symbol was never referenced, or was
+		  /* Do nothing.  The symbol was never referenced, or
-		     defined by some object.  */
+		     was defined in some object file.  Undefined weak
+		     symbols stay undefined.  */
 		  break;
 		}
 	    }

ld/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2014-12-23  Alan Modra  <amodra@gmail.com>
+
+	* ld-elf/endsym.s, *ld-elf/endsym.d: New test.
+
 2014-12-19  Matthew Fortune  <matthew.fortune@imgtec.com>
 
 	* ld-mips-elf/attr-gnu-4-00.d: Relax check for ISA extension.

ld/testsuite/ld-elf/endsym.d

@@ -0,0 +1,13 @@
+#source: start.s
+#source: endsym.s
+#ld: --sort-common
+#nm: -n
+#notarget: hppa*-*-hpux*
+
+#...
+.* end
+#...
+.* end2
+#...
+.* _?_end
+#pass

ld/testsuite/ld-elf/endsym.s

@@ -0,0 +1,2 @@
+ .comm end,4,4
+ .comm end2,2,2