targetm.init_builtins and build_common_builtin_nodes ordering

[Mike Stump]

So, in c-common.c we have:

  targetm.init_builtins ();
  build_common_builtin_nodes ();

and in f95-1.c we have:

  build_common_builtin_nodes ();
  targetm.init_builtins ();

I would like to change c-common.c to match fortran, so that the target hook can 
slightly alter (rename) the linkage name of some of the common builtin nodes.  
If that answer is no, what's the best way to get __divdc3 renamed?

Thoughts?