RFR: 8318692: Add instructions for creating Ubuntu-based sysroot for cross compilation [v3]

[Aleksey Shipilev]

On Tue, 24 Oct 2023 13:03:51 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 incrementally with two additional commits since the last revision:
> 
>  - Update rendered HTML
>  - Update building.md

Marked as reviewed by shade (Reviewer).

doc/building.md line 1206:

> 1204:       ~/sysroot-arm64 \
> 1205:       http://ports.ubuntu.com/ubuntu-ports/
> 1206:     # symlinks is in the universe repository

I am not a fan of doing comments in the "executable" code blocks, but I guess this is innocuous.

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PR Review: https://git.openjdk.org/jdk/pull/16331#pullrequestreview-1695079683
PR Review Comment: https://git.openjdk.org/jdk/pull/16331#discussion_r1370312770