psxmsgq01/init.c: Disable signal usage when POSIX disabled

closes #3626.

testsuites/psxtests/psxmsgq01/init.c

@@ -910,6 +910,7 @@ void wait_for_signal(
   int           expect_signal
 )
 {
+#if defined(RTEMS_POSIX_API)
   siginfo_t         siginfo;
   int               status;
   struct timespec   timeout;
@@ -936,6 +937,7 @@ void wait_for_signal(
     fatal_int_service_status( signo, -1, "error return status");
     fatal_posix_service_status( errno, EAGAIN, "errno EAGAIN");
   }
+#endif
 }
 
 void verify_notify(void)