8207340: (fs) UnixNativeDispatcher close and readdir usages should be fixed

[Alan Bateman]

The issue of restarting close when interrupted was discussed recently on 
serviceability-dev and fixed via JDK-8206145. At the same time, there 
are several threads about the changes in JDK-8202353 to fix the usages 
of readdir_r in HotSpot as that function is deprecated in recent 
releases of glibc. There are equivalent changes needed in the JNI code, 
currently tracked as JDK-8202794. One sub-task is the usages in 
src/java.base/unix/native/libnio/UnixNativeDispatcher.c which is easy to 
fix with the following patch:

http://cr.openjdk.java.net/~alanb/8207340/webrev/index.html

The readdir change is the same as the patch I sent to Bernard Blasser on 
core-libs-dev a few weeks ago. I've tested this on macOS, Linux, and 
Solaris.

-Alan