Don't copy const0_rtx to a CONCAT in emit_group_store

[Richard Kenner]

This will normally cause an ICE, but is not helpful in any case.
The ICEs were seen in numerous Ada ACATS tests on ia64.

Tested on ia64.

Thu Mar 21 09:50:48 2002  Richard Kenner  <kenner@vlsi1.ultra.nyu.edu>

	* expr.c (emit_group_store): Don't copy const0_rtx to a CONCAT.

*** expr.c	2002/03/19 21:17:34	1.423.2.7
--- expr.c	2002/03/20 19:12:34
*************** emit_group_store (orig_dst, src, ssize)
*** 2101,2105 ****
        return;
      }
!   else if (GET_CODE (dst) != MEM)
      {
        dst = gen_reg_rtx (GET_MODE (orig_dst));
--- 2101,2105 ----
        return;
      }
!   else if (GET_CODE (dst) != MEM && GET_CODE (dst) != CONCAT)
      {
        dst = gen_reg_rtx (GET_MODE (orig_dst));