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/syscall.c b/syscall.c
index 01e4b31..c61f827 100644
--- a/syscall.c
+++ b/syscall.c
@@ -1042,7 +1042,7 @@
 				else
 					tprintf("= %ld", tcp->u_rval);
 				break;
-#if defined(LINUX_MIPSN32) || defined(X32)
+#if HAVE_STRUCT_TCB_EXT_ARG
 			/*
 			case RVAL_LHEX:
 				tprintf("= %#llx", tcp->u_lrval);
@@ -1059,7 +1059,7 @@
 				tprintf("= %lld", tcp->u_lrval);
 				break;
 			*/
-#endif
+#endif /* HAVE_STRUCT_TCB_EXT_ARG */
 			default:
 				error_msg("invalid rval format");
 				break;