JDK-8253947: JEP 388 Windows/AArch64 backport to jdk11u

[Bernhard Urban-Forster]

Hello,

Spinning off the discussion from here: https://github.com/openjdk/jdk/pull/2200#issuecomment-804927150

And further context, there have been some discussions about it before:
https://mail.openjdk.java.net/pipermail/aarch64-port-dev/2020-October/009727.html


Open questions:

1. JEP 391 (macOS/AArch64) has a dependency on JEP 388, and I'm assuming we want both to be backported.  Question: Is it preferred to do it one go (both together), or should we do it separately (that would be Windows first, then macOS)?

2. JEP 388 includes build changes to add cross compilation support for Windows in a hacky way. It's enough to get a build out of it [1], but it's not exactly clean. It was eventually cleaned up with the "WINENV" patch by Magnus [2], but imho it isn't trivial to backport that change.  Thoughts?


Assuming the answer to question 1 is to split the backports: I think https://github.com/openjdk/aarch64-port/tree/jdk11-windows by Ludovic is in an okay shape, but I will take it for a spin tomorrow and then submit an initial PR against https://github.com/openjdk/jdk11u


Thank you,
-Bernhard


[1] with workarounds: https://github.com/openjdk/jdk/pull/212#issuecomment-695024586
[2] https://github.com/openjdk/jdk/pull/1597