Handle OpenSSL without dynamic ENGINE

[bneradt]

Some OpenSSL builds expose the async APIs ATS can use while disabling the legacy ENGINE interface. On those platforms, such as RHEL 10, the test-only async_engine plugin fails to compile even though runtime TLS async support can still be built without it.

This adds a CMake compile check for dynamic ENGINE availability and uses it to gate the test plugin. The TLS engine AuTest now skips when the test plugin was not built, while ENGINE-capable builds continue to build and run the test.

[Copilot]

Pull request overview

This PR improves build/test portability for OpenSSL configurations that provide async TLS APIs but disable the legacy dynamic ENGINE interface (e.g., some distro builds). It prevents the test-only async_engine AuTest plugin from being built when dynamic ENGINE isn’t available, and updates the TLS engine gold test to skip cleanly in that scenario.

Changes:

• Add a CMake compile probe (HAVE_OPENSSL_DYNAMIC_ENGINE) to detect OpenSSL dynamic ENGINE availability.
• Gate building/linking the async_engine AuTest plugin on both TS_USE_TLS_ASYNC and HAVE_OPENSSL_DYNAMIC_ENGINE.
• Update the tls_engine gold test to skip unless the async_engine.so test plugin exists, and reuse the computed plugin path for the copy step.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
CMakeLists.txt	Adds a compile-time probe for OpenSSL dynamic ENGINE support (HAVE_OPENSSL_DYNAMIC_ENGINE).
tests/tools/plugins/CMakeLists.txt	Builds the async_engine AuTest plugin only when async TLS is enabled and dynamic ENGINE is available.
tests/gold_tests/tls/tls_engine.test.py	Skips the test when async_engine.so wasn’t built and avoids repeating the plugin path.