The fix for 8030046, is incorrect and the problem is two fold.

wrt. http://hg.openjdk.java.net/jdk9/dev/langtools/rev/e6e9f1b096c8

On Windows toURI().resolve will fail with:
[STDOUT]:
java.lang.IllegalArgumentException: Illegal character in opaque part at index 2: C:\cygwin\BLAH\scratch\jars\test.jar

The IAE unfortunately is swallowed, as follows:
+ try {
+ File f = parent == null ? new File(elt): new File(file.toURI().resolve(elt));
+ list.add(f);
+ } catch (IllegalArgumentException ex) {}

So thus the jar will never be added to the classpath on Windows, because of the
drive specifier "c:".

Secondly the test is flawed, in the original changeset:
The path name to the jar created in line 2.55 is never added to the args, thus
the test never worked on any platform, and this was masked because only
"-cp ." was used.

The issue was unmasked by the fix for JDK-8050429, now the test seems to be
working correctly but fails on Windows.