JDK-8215445: Enable building for Windows in WSL

[Andrew Luo]

Glad to see this moving forward, and thanks for your help with getting this working as well.  I didn't look at my own changes, but the extra work you added to fix spaces, docs, and Cygwin look good to me (not a reviewer though).  Thanks for helping with getting this in!

One small thing - do you think we should change the building.md to note using 1809 is recommended (or required?) due to the issue with make, or do you want to put it out there first to see if others have the same issue? 

Thanks,

-Andrew

-----Original Message-----
From: Erik Joelsson <erik.joelsson at oracle.com> 
Sent: Thursday, December 20, 2018 4:48 AM
To: build-dev <build-dev at openjdk.java.net>; Andrew Luo <andrewluotechnologies at outlook.com>
Subject: RFR: JDK-8215445: Enable building for Windows in WSL

Hello,

Thanks to huge help from Andrew Luo, we now have a patch that adds support for building OpenJDK for Windows using WSL as the Unix layer instead of Cygwin. I have made some adjustments, mostly to keep it working in Cygwin. I have also run it through some testing, mostly to make sure there are no regressions to the current Cygwin support. This includes a COMPARE run which showed no regressions as well as comparing a WSL and Cygwin build, which showed no unexpected differences.

I'm happy to see that on my Windows Workstation, the time to run "make bundles" is considerably faster in WSL, about 8m40s compared to 12m55s.

It should be noted that testing is still not fully supported. We will likely need to adjust some tests to work correctly in WSL and it's also possible that jtreg will also need adjustments.

(For internal Oracle developers, Jib does not support WSL yet)

Bug: https://bugs.openjdk.java.net/browse/JDK-8215445

Webrev: http://cr.openjdk.java.net/~erikj/8215445/webrev.02/index.html

/Erik