fix gcc bug #34130 (wrong multiplication with negative constants

inside abs()) which got some attention in the linux kernel mailing
list recently

gnu/dist/gcc4/gcc/fold-const.c

@@ -5340,6 +5340,9 @@ extract_muldiv_1 (tree t, tree c, enum tree_code code, tree wide_type)
             }
           break;
         }
+      /* If the constant is negative, we cannot simplify this.  */ 
+      if (tree_int_cst_sgn (c) == -1)
+	break;
       /* FALLTHROUGH */
     case NEGATE_EXPR:
       if ((t1 = extract_muldiv (op0, c, code, wide_type)) != 0)