Bug #55345, "mysql_library_init causes segfault if executed after calling mysql_library_end"

my_thread_global_end() now sets mysql_thread_basic_global_init_done= 0
to ensure destroyed mutexes are not reused.

I verified that clearing this flag will not result in the redundant allocation
of other resources allocated by my_thread_global_init() and
my_thread_basic_global_init().

mysys/my_thr_init.c:
  Clear mysql_thread_basic_global_init_done flag at the end of my_thread_global_end()

mysys/my_thr_init.c

@@ -302,6 +302,8 @@ void my_thread_global_end(void)
 #ifndef HAVE_GETHOSTBYNAME_R
   mysql_mutex_destroy(&LOCK_gethostbyname_r);
 #endif
+
+  my_thread_basic_global_init_done= 0;
 }
 
 static my_thread_id thread_id= 0;