new macro: thread_safe_decrement, thread_safe_dec_and_test, statistic_decrement


mysys/my_chsize.c:
  cleanup
include/config-win.h:
  mmap portability layer, mmap for Windows
include/my_pthread.h:
  thread_safe_decrement, thread_safe_dec_and_test, statistic_decrement
include/my_sys.h:
  mmap portability layer, mmap for Windows
mysys/Makefile.am:
  mmap portability layer, mmap for Windows