* system.h: Poison ASM_SIMPLIFY_DWARF_ADDR.

        * varasm.c (lookup_constant_def): New function.
        * rtl.h (lookup_constant_def): Declare it.
        * dwarf2out.c (loc_descriptor_from_tree): Use it.
        Use targetm.delegitimize_address, not ASM_SIMPLIFY_DWARF_ADDR.

From-SVN: r70072