RFR: 8287325: AArch64: fix virtual threads with -XX:UseBranchProtection=pac-ret

[Nick Gasson]

On Wed, 8 Jun 2022 13:04:15 GMT, Nick Gasson <ngasson at openjdk.org> wrote:

> 
> For now I can make another patch that disables PAC-RET when `Arguments::enable_preview()` is true.

See #9102

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PR: https://git.openjdk.java.net/jdk/pull/9067