Introduce HAVE_STRUCT_TCB_EXT_ARG macro

Check for "if HAVE_STRUCT_TCB_EXT_ARG" instead of
"if defined LINUX_MIPSN32 || defined X32".

* defs.h (HAVE_STRUCT_TCB_EXT_ARG): Define for LINUX_MIPSN32 || X32.
(struct tcb): Check it instead of LINUX_MIPSN32 || X32.
(RVAL_LUDECIMAL): Likewise.
* io.c (print_lld_from_low_high_val): Likewise.
* lseek.c (SYS_FUNC(lseek)): Likewise.
* mem.c (SYS_FUNC(mmap)): Likewise.
* syscall.c (trace_syscall_exiting): Likewise.
* util.c (getllval): Likewise.
diff --git a/util.c b/util.c
index ea2e869..bb23eeb 100644
--- a/util.c
+++ b/util.c
@@ -257,16 +257,16 @@
 # endif /* SUPPORTED_PERSONALITIES > 1 */
 #elif SIZEOF_LONG > 4
 #  error Unsupported configuration: SIZEOF_LONG > 4 && SIZEOF_LONG_LONG > SIZEOF_LONG
-#elif defined LINUX_MIPSN32
-	*val = tcp->ext_arg[arg_no];
-	arg_no++;
-#elif defined X32
-	if (current_personality == 0) {
-		*val = tcp->ext_arg[arg_no];
-		arg_no++;
-	} else {
+#elif HAVE_STRUCT_TCB_EXT_ARG
+# if SUPPORTED_PERSONALITIES > 1
+	if (current_personality == 1) {
 		*val = LONG_LONG(tcp->u_arg[arg_no], tcp->u_arg[arg_no + 1]);
 		arg_no += 2;
+	} else
+# endif
+	{
+		*val = tcp->ext_arg[arg_no];
+		arg_no++;
 	}
 #else
 # if defined __ARM_EABI__ || \