RFR: 8318692: Add instructions for creating Ubuntu-based sysroot for cross compilation [v4]

[Aleksey Shipilev]

On Tue, 24 Oct 2023 23:15:54 GMT, Zixian Cai <zcai at openjdk.org> wrote:

>> Sometimes it's useful to have a Ubuntu-based chroot when you want to ensure compatibility of your deployment target and/or have access to packages that might not be in Debian upstream for some architectures.
>> 
>> Ubuntu-based sysroot warrants a separate instruction because `symlinks` is in the `universe` repository, and without that, `debootstrap` might fail with package not found, but it's not immediately obvious why.
>> 
>> This should be merged after #16332 for consistent formatting. Once #16332 is merged, I will update this PR.
>
> Zixian Cai has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:
> 
>  - Merge master
>  - Update rendered HTML
>  - Update building.md
>  - Update rendered HTML
>  - Add instructions for creating Ubuntu-based sysroot for cross compilation

Marked as reviewed by shade (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/16331#pullrequestreview-1696695180