FW: RFR: 8285630: Fix a configure error in RISC-V cross build

[Pengfei Li]

Hi,

May I have a review of this fix for RISC-V cross build?
https://github.com/openjdk/jdk/pull/8420

> We are trying to cross build a RISC-V version of OpenJDK. We specified `--
> openjdk-target=riscv64-linux-gnu` after `bash configure` but got an error
> message.
> 
> 
> configure: error: /usr/bin/bash /home/ent-
> user/jdk_src/make/autoconf/build-aux/config.sub riscv64-linux-gnu failed
> configure exiting with result code 1
> 
> 
> It shows the processing of `riscv64-linux-gnu` in script `config.sub` fails. We
> see `config.sub` calls another script `autoconf-config.sub` to validate and
> canonicalize a configuration type. The validation fails here because
> `autoconf-config.sub` is a quite old version and has no RISC-V support inside.
> Comments in those scripts tell us patching the autoconf script is not a good
> idea so we add a fix in `config.sub` in this patch.
> 
> We have verified RISC-V cross build succeeds after this change. As we are not
> quite familiar with the build system, please let us know if this is the best way
> to fix.
> 
> -------------
> 
> Commit messages:
>  - 8285630: Fix a configure error in RISC-V cross build
> 
> Changes: https://git.openjdk.java.net/jdk/pull/8420/files
>  Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8420&range=00
>   Issue: https://bugs.openjdk.java.net/browse/JDK-8285630
>   Stats: 8 lines in 1 file changed: 7 ins; 0 del; 1 mod
>   Patch: https://git.openjdk.java.net/jdk/pull/8420.diff
>   Fetch: git fetch https://git.openjdk.java.net/jdk pull/8420/head:pull/8420
> 
> PR: https://git.openjdk.java.net/jdk/pull/8420

--
Thanks,
Pengfei