Fix inline_merge_summary ICE during kernel build

[Jan Hubicka]

Hi,
the problem is that Andi's test build is with -O0 and we should not allocate
ipa-prop datastructures then. We do so via duplication hook by accident since
do_whole_program_analysis for some illogical reason calls
ipa_register_cgraph_hooks.

Comitted as obvoius.
Honza
        PR lto/48952
        * lto.c (do_whole_program_analysis): Do not register cgraph hooks.

Index: lto/lto.c
===================================================================
--- lto/lto.c   (revision 173666)
+++ lto/lto.c   (working copy)
@@ -2511,7 +2511,6 @@ do_whole_program_analysis (void)
       dump_varpool (cgraph_dump_file);
     }
   bitmap_obstack_initialize (NULL);
-  ipa_register_cgraph_hooks ();
   cgraph_state = CGRAPH_STATE_IPA_SSA;
 
   execute_ipa_pass_list (all_regular_ipa_passes);