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()