[jdk11u-dev] RFR: 8265343: Update Debian-based cross-compilation recipes [v2]

[Aleksey Shipilev]

> Another (hopefully final) backport to improve cross-compilation docs. The simplified cross-compilation recipe matches what we have in 11u GHA: only `--openjdk-target` and `--with-sysroot` is supplied.
> 
> It had minor contextual conflicts that precluded the automatic merge. I checked that the platforms listed in compatible platforms list is indeed buildable (see https://builds.shipilev.net/openjdk-jdk11-dev/ for example).

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into JDK-8265343-update-debian
 - Backport 7879adbe88ec54b8f5ac9543d80142bc1b12112b

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk11u-dev/pull/601/files
  - new: https://git.openjdk.java.net/jdk11u-dev/pull/601/files/a2e1eb1b..e4c8a9ea

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=601&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=601&range=00-01

  Stats: 417188 lines in 3268 files changed: 205540 ins; 208609 del; 3039 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/601.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/601/head:pull/601

PR: https://git.openjdk.java.net/jdk11u-dev/pull/601