Since post4 catches SIGTERM, set the exit code to the same value

the shell would use, ie. 128 + signal.

src/post4.c

@@ -1519,6 +1519,7 @@ p4Repl(P4_Ctx *ctx)
 			/* Historically no message, simply return to REPL. */
 			break;
 		case P4_THROW_TERMINATE:
+			rc = 128 + SIGTERM;
 			(void) printf(crlf);
 			goto setjmp_cleanup;
 		default: