Decode TLS syscalls on m68k

* linux/m68k/syscallent.h: Add entries for get_thread_area,
set_thread_area, atomic_comxchg_32, atomic_barrier.
* linux/dummy.h (sys_get_thread_area, sys_set_thread_area) [M68K]:
Don't redefine.
* mem.c (sys_get_thread_area, sys_set_thread_area) [LINUX && M68K]: New.
diff --git a/linux/dummy.h b/linux/dummy.h
index 92e6886..ce81649 100644
--- a/linux/dummy.h
+++ b/linux/dummy.h
@@ -41,9 +41,11 @@
 /* machine-specific */
 #ifndef I386
 #define	sys_modify_ldt		printargs
+#ifndef M68K
 #define sys_get_thread_area	printargs
 #define sys_set_thread_area	printargs
 #endif
+#endif
 
 #define sys_sched_yield		printargs
 #define sys_sched_get_priority_max sys_sched_get_priority_min