[11u] RFR 8191521: handle long relative path specified in -Xbootclasspath/a on windows

[Schmelter, Ralf]

I'd like to backport the change to 11u-dev:

bugreport: https://bugs.openjdk.java.net/browse/JDK-8191521
change: https://hg.openjdk.java.net/jdk/jdk/rev/ed5e399d967d
webrev: http://cr.openjdk.java.net/~rschmelter/webrevs/8191521/webrev.jdk11u-dev.01/

The patch had to be modified since it also adjusted the os:: same_files() method, which is not present in JDK11.
Otherwise it applied cleanly.

This change includes the following fixes too:

bugreport fix 1: https://bugs.openjdk.java.net/browse/JDK-8231930
change fix 1: https://hg.openjdk.java.net/jdk/jdk/rev/74094a60d018
bugreport fix 2: https://bugs.openjdk.java.net/browse/JDK-8231885
change fix 2: https://hg.openjdk.java.net/jdk/jdk/rev/b1da055915ef

Best regards,
Ralf