hg: jdk/hs: 8192927: os::dir_is_empty is incorrect on Windows

[calvin.cheung at oracle.com]

Changeset: 4d7a4fad8190
Author:    ccheung
Date:      2018-01-04 22:47 -0800
URL:       http://hg.openjdk.java.net/jdk/hs/rev/4d7a4fad8190

8192927: os::dir_is_empty is incorrect on Windows
Summary: Check file names in a directory. It is empty if only the "." and ".." files exist. Use unicode version of windows APIs to handle long path.
Reviewed-by: iklam, sspitsyn

! src/hotspot/os/windows/os_windows.cpp
! test/hotspot/jtreg/runtime/appcds/DirClasspathTest.java