RFR: 8351322: Parameterize link option for pthreads

[David Holmes]

On Thu, 6 Mar 2025 10:39:27 GMT, snake66 <duke at openjdk.org> wrote:

> Replace hardcoded instances of `-lpthread` with `$(LIBPTHREAD)`, so that it's possible to parameterize this for platforms that use different flags for enabling posix threads.
> 
> This work is a continuation of the work done by Greg Lewis in [1], but generalized for the full JDK, and set at the configure stage.
> 
> Sponsored by: The FreeBSD Foundation
> Co-authored-by: Greg Lewis <glewis at eyesbeyond.com>
> 
> [1]: https://github.com/battleblow/jdk23u/commit/dbd90aa8ab0b7f5e4865864a7c63d975daacabf4

Abstracting this out seems reasonable to me, though I should say I thought we already used `-pthread` rather than `-lpthread`.

Needs build team approval before integrating.

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23930#pullrequestreview-2664340896