linux-user: Enable NPTL for m68k

For m68k, per-thread data is a purely kernel construct with no
CPU level support. Implement it via a field in the TaskState structure,
used by cpu_set_tls() and the set_thread_area/get_thread_area
syscalls. This allows us to enable compilation with NPTL.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by:  Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 00a0390..9619656 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8558,6 +8558,12 @@
 #elif defined(TARGET_I386) && defined(TARGET_ABI32)
       ret = do_set_thread_area(cpu_env, arg1);
       break;
+#elif defined(TARGET_M68K)
+      {
+          TaskState *ts = ((CPUArchState *)cpu_env)->opaque;
+          ts->tp_value = arg1;
+          break;
+      }
 #else
       goto unimplemented_nowarn;
 #endif
@@ -8566,6 +8572,12 @@
     case TARGET_NR_get_thread_area:
 #if defined(TARGET_I386) && defined(TARGET_ABI32)
         ret = do_get_thread_area(cpu_env, arg1);
+#elif defined(TARGET_M68K)
+        {
+            TaskState *ts = ((CPUArchState *)cpu_env)->opaque;
+            ret = ts->tp_value;
+            break;
+        }
 #else
         goto unimplemented_nowarn;
 #endif