RFR: 8375094: RISC-V: Fix client builds after JDK-8368732

[Feilong Jiang]

On Tue, 13 Jan 2026 04:54:39 GMT, Dingli Zhang <dzhang at openjdk.org> wrote:

> Hi,
> Can you help to review this patch? Thanks!
> 
> [JDK-8368732](https://bugs.openjdk.org/browse/JDK-8368732) broke RISC-V client builds because `AlignVector` is a C2-only option.
> This pr is to put `AlignVector` under COMPILER2 macro protection.
> 
> Builds tested w/ and w/o `--with-jvm-variants=client`.

Thanks!

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Marked as reviewed by fjiang (Committer).

PR Review: https://git.openjdk.org/jdk/pull/29182#pullrequestreview-3654232765