Bug#54334 Double initialization of mysys mutexes

Prior to this fix, mysys mutexes such as THR_LOCK_lock could be initialized
twice by a call to my_init().
The root cause was out of place initialization in my_basic_init(),
calling my_thread_global_init().

With this fix,
- my_basic_init() properly initializes the mutex implementation itself,
for SAFE or FAST mutexes, and for platform dependent initializations,
before initialiazing a mutex.
- my_init() properly initializes mysys mutexes once,
when making the first call to my_thread_global_init().

mysys/my_init.c

@@ -104,8 +104,6 @@ my_bool my_basic_init(void)
   mysql_stdin= & instrumented_stdin;
 
 #if defined(THREAD)
-  if (my_thread_global_init())
-    return 1;
 #  if defined(SAFE_MUTEX)
   safe_mutex_global_init();		/* Must be called early */
 #  endif