RFR: JDK-8225140: Build fails if directory contains 'unix'

[Erik Joelsson]

If the workspace directory (or any parent) contains the word "unix", the 
build fails in java.desktop-libs. There are several libraries here that 
use the EXCLUDE_SRC_FILTER option of SetupJdkLibrary to filter away the 
src/java.desktop/unix/lib* dirs. This option incorrectly includes the 
whole absolute path of each source file when applying the filter, so 
when the workspace dir contains "unix", these libraries get no source 
files at all.

This patch changes the filter mechanics to only apply to the path 
relative to the workspace root. I also changed the filter token from 
"unix" to "/unix/" to avoid the risk of matching substrings in 
directories in the future.

Bug: https://bugs.openjdk.java.net/browse/JDK-8225140

Webrev: http://cr.openjdk.java.net/~erikj/8225140/webrev.01/index.html

/Erik