RFR: Replace BacktraceBuilder and allocation safepoints in async_get_stack_trace [v4]

[Coleen Phillimore]

On Thu, 6 May 2021 12:49:34 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Something like this.  I'm still running tests.
>
> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove 2 stack trace tests that now pass.

Thanks Serguei.  Can someone sponsor?

-------------

PR: https://git.openjdk.java.net/loom/pull/40