m68k, linux-user: enable sigaltstack()

As setup_frame() and setup_rt_frame() are now implemented we can now
enable sigaltstack().
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>
Signed-off-by: NRiku Voipio <riku.voipio@iki.fi>

linux-user/syscall.c

@@ -6111,7 +6111,8 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
         goto unimplemented;
     case TARGET_NR_sigaltstack:
 #if defined(TARGET_I386) || defined(TARGET_ARM) || defined(TARGET_MIPS) || \
-    defined(TARGET_SPARC) || defined(TARGET_PPC) || defined(TARGET_ALPHA)
+    defined(TARGET_SPARC) || defined(TARGET_PPC) || defined(TARGET_ALPHA) || \
+    defined(TARGET_M68K)
         ret = do_sigaltstack(arg1, arg2, get_sp_from_cpustate((CPUState *)cpu_env));
         break;
 #else