internal-fn: Fix up expand_arith_overflow [PR114753]

During backporting I've noticed I've missed one return spot for the
restoration of the original flag_trapv flag value.

2024-04-19  Jakub Jelinek  <[email protected]>

	PR middle-end/114753
	* internal-fn.cc (expand_arith_overflow): Add one missing restore
	of flag_trapv before return.

Author: jakubjelinek

gcc/internal-fn.cc

@@ -2793,6 +2793,7 @@ expand_arith_overflow (enum tree_code code, gimple *stmt)
 	    case PLUS_EXPR:
 	      expand_addsub_overflow (loc, code, lhs, arg0, arg1, unsr_p,
 				      unsr_p, unsr_p, false, NULL);
+	      flag_trapv = save_flag_trapv;
 	      return;
 	    case MULT_EXPR:
 	      expand_mul_overflow (loc, lhs, arg0, arg1, unsr_p,