replaced syscall with find_thread(NULL) to obtain current thread id

currently, find_thread(NULL) also uses a syscall, but in the future,
this will be implemented as an efficient inline lookup in calling
thread's local storage


git-svn-id: file:///srv/svn/repos/haiku/trunk/current@2017 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/kernel/libroot/posix/signal/raise.c

@@ -19,8 +19,6 @@
 int
 raise(int sig)
 {	
-	thread_id tid = sys_get_current_thread_id();
-	
-	return sys_send_signal(tid, sig);
+	return sys_send_signal(find_thread(NULL), sig);
 }