RFR: JDK-8305118: Add RISC-V related content to building.md

[Guoxiong Li]

On Wed, 29 Mar 2023 10:28:37 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> RISC-V cross-compiles with sysroots fine: https://builds.shipilev.net/openjdk-jdk/configure-logs/configure-openjdk-jdk-linux-riscv64-server-release-gcc10-glibc2.31.log https://builds.shipilev.net/openjdk-jdk/build-logs/build-openjdk-jdk-linux-riscv64-server-release-gcc10-glibc2.31.log
> 
> Sometimes you need to point to tools like `OBJCOPY` and `STRIP`, if the host/target triplets contain `unknown`. But other than that, it should be pretty straight-forward.

Thanks for the tips. I know why I failed locally now. The mirror path should be `debian-ports` instead of `debian`. `http://deb.debian.org/debian-ports` and `http://httpredir.debian.org/debian-ports` succeed. The file [.github/workflows/build-cross-compile.yml](https://github.com/openjdk/jdk/blob/b3ff8d1c89b0f968b7b5ec2105502778524e4e4a/.github/workflows/build-cross-compile.yml#L89) provides the concrete information.

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PR Comment: https://git.openjdk.org/jdk/pull/13223#issuecomment-1489665270