RFR: 8350667: Remove startThread_lock() and _startThread_lock on AIX

[Joachim Kern]

On Tue, 25 Feb 2025 15:58:36 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> The startThread_lock() and _startThread_lock coding is not used on AIX so it can be removed.

LGTM

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

Marked as reviewed by jkern (Committer).

PR Review: https://git.openjdk.org/jdk/pull/23779#pullrequestreview-2643964881