Merge branch 'js/win32-mmap'

Merge branch 'js/win32-mmap'

mmap emulation on Windows has been optimized and work better without
consuming paging store when not needed.

* js/win32-mmap:
  mmap(win32): avoid expensive fstat() call
  mmap(win32): avoid copy-on-write when it is unnecessary
  win32mmap: set errno appropriately