[sledge] Add missing llvm passes to frontend.ml

Summary:
Adds `-mergefunc` and `-dce` passes to `Frontend.translate` to match
the `buck link` flow with `opt`

Reviewed By: ngorogiannis

Differential Revision: D15938641

fbshipit-source-id: 128cb89cd

sledge/src/llair/frontend.ml

@@ -1362,10 +1362,12 @@ let transform : Llvm.llmodule -> unit =
       List.exists entry_points ~f:(String.equal fn) ) ;
   Llvm_ipo.add_global_dce pm ;
   Llvm_ipo.add_global_optimizer pm ;
+  Llvm_ipo.add_merge_functions pm ;
   Llvm_ipo.add_constant_merge pm ;
   Llvm_ipo.add_argument_promotion pm ;
   Llvm_ipo.add_ipsccp pm ;
   Llvm_scalar_opts.add_memory_to_register_promotion pm ;
+  Llvm_scalar_opts.add_dce pm ;
   Llvm_ipo.add_global_dce pm ;
   Llvm_ipo.add_dead_arg_elimination pm ;
   Llvm_scalar_opts.add_lower_atomic pm ;