RFR: 8283929: GHA: Add RISC-V build config [v2]

[Ludovic Henry]

> It adds CI for cross-compiling to linux-riscv64. It requires to use Ubuntu repositories for the debootstrap image because Debian doesn't have riscv64 packages on https://httpredir.debian.org/debian/. We can follow up on this change with switching to http://ports.ubuntu.com/ubuntu-ports for all cross-compiled architectures.
> 
> This change also does not require nor blocks switching to Ubuntu 22.04.
> 
> From talking with @shipilev, this replaces https://github.com/openjdk/jdk/pull/10086.

Ludovic Henry has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:

 - Merge branch 'master' of https://github.com/openjdk/jdk into dev/ludovic/ci-cross-compile-riscv64
 - Add cross-compilation to riscv64 on CI

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Changes: https://git.openjdk.org/jdk/pull/10168/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10168&range=01
  Stats: 33 lines in 1 file changed: 25 ins; 5 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/10168.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10168/head:pull/10168

PR: https://git.openjdk.org/jdk/pull/10168