RFR: 8285692: Enable _FORTIFY_SOURCE=2 when building with Clang

[Erik Joelsson]

On Thu, 5 Dec 2024 22:21:43 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

> Clang has supported _FORTIFY_SOURCE since version 10. We already use it when building with gcc ([JDK-8130017](https://bugs.openjdk.org/browse/JDK-8130017)) in fastdebug builds. We should add it to fastdebug builds with Clang.
> 
> I solved this by unifying the clang/gcc flag setup.

Marked as reviewed by erikj (Reviewer).

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

PR Review: https://git.openjdk.org/jdk/pull/22586#pullrequestreview-2483168650