expr.c: don't assume MUL for scaling pointers

[DJ Delorie]

GCC assumes the target has a multiply insn, but better code is
generated using shifts if it doesn't (vs a libcall).  Found with the
rl78-elf port.

        * expr.c (expand_expr_real_2): Don't try to emit a MUL-based
        expression if the target doesn't have a multiply pattern.  Fall
        back to shifts instead of using libgcc calls.

Index: gcc/expr.c
===================================================================
--- gcc/expr.c  (revision 180758)
+++ gcc/expr.c  (working copy)
@@ -8289,12 +8289,13 @@ expand_expr_real_2 (sepops ops, rtx targ
        }
 
       /* Attempt to return something suitable for generating an
         indexed address, for machines that support that.  */
 
       if (modifier == EXPAND_SUM && mode == ptr_mode
+         && optab_handler (smul_optab, mode) != CODE_FOR_nothing
          && host_integerp (treeop1, 0))
        {
          tree exp1 = treeop1;
 
          op0 = expand_expr (treeop0, subtarget, VOIDmode,
                             EXPAND_SUM);