RFR: 8282475: SafeFetch should not rely on existence of Thread::current [v4]

[Johannes Bechberger]

On Tue, 8 Mar 2022 10:32:46 GMT, Johannes Bechberger <duke at openjdk.java.net> wrote:

>> The WXMode for the current thread (on MacOS aarch64) is currently stored in the thread class which is unnecessary as the WXMode is bound to the current OS thread, not the current instance of the thread class.
>> This pull request moves the storage of the current WXMode into a thread local global variable in `os` and changes all related code. SafeFetch depended on the existence of a thread object only because of the WXMode. This pull request therefore removes the dependency, making SafeFetch usable in more contexts.
>
> Johannes Bechberger has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Move code to os::current_thread_wx
>  - Small fixes

I don't know why the Linux x86 build fails.

I tested the current version with code related to #7591 and it seems to fix the remaining problems (I tested it also with NMT enabled).

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

PR: https://git.openjdk.java.net/jdk/pull/7727