Small PATCH to rs6000.c to fix cross-compiler build without gas

[Jason Merrill]

If configure doesn't think that the assembler supports weak symbols, 
rs6000.c fails to compile because ASM_WEAKEN_DECL isn't defined.  So 
let's not use it in that case.

OK for trunk?
commit 5f0878b79d1a42795aca2fabc8d70eefa2e29fa6
Author: Jason Merrill <ja...@redhat.com>
Date:   Wed Oct 3 15:55:48 2012 -0400
    	* config/rs6000/rs6000.c (rs6000_code_end): Protect the use of
    	ASM_WEAKEN_DECL with #if RS6000_WEAK.

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 3e3d553..f4e4dec 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -28295,6 +28295,7 @@ rs6000_code_end (void)
   TREE_PUBLIC (decl) = 1;
   TREE_STATIC (decl) = 1;
 
+#if RS6000_WEAK
   if (USE_HIDDEN_LINKONCE)
     {
       DECL_COMDAT_GROUP (decl) = DECL_ASSEMBLER_NAME (decl);
@@ -28307,6 +28308,7 @@ rs6000_code_end (void)
       ASM_DECLARE_FUNCTION_NAME (asm_out_file, name, decl);
     }
   else
+#endif
     {
       switch_to_section (text_section);
       ASM_OUTPUT_LABEL (asm_out_file, name);