RFR: 8318692: Add instructions for creating Ubuntu-based sysroot for cross compilation [v2]

[Zixian Cai]

> 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.

Zixian Cai has updated the pull request incrementally with one additional commit since the last revision:

  Update rendered HTML

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16331/files
  - new: https://git.openjdk.org/jdk/pull/16331/files/7bb8f469..3148ecda

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16331&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16331&range=00-01

  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16331.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16331/head:pull/16331

PR: https://git.openjdk.org/jdk/pull/16331