optimized build failed with the following error message.

```
=== Output from failing command(s) repeated here ===
* For target hotspot_variant-server_libjvm_objs_continuation.o:
/home/runner/work/loom/loom/jdk/src/hotspot/share/runtime/continuation.cpp:3055:13: error: 'void print_frames(JavaThread*, outputStream*)' defined but not used [-Werror=unused-function]
 3055 | static void print_frames(JavaThread* thread, outputStream* st) {
      | ^~~~~~~~~~~~
cc1plus: all warnings being treated as errors

* All command lines available in /home/runner/work/loom/loom/jdk/build/linux--hotspot/make-support/failure-logs.
=== End of repeated output ===
```

I suppose this failure was introduced in commit 4d2710 (link: https://github.com/openjdk/loom/commit/4d2710#diff-74c5a41cb3476b29151b4a13732cf4756879de0aa1b1d8c4d73c38e570413fcfR2851)

In commit 4d2710, one invocation of function print_frames() is moved from "! PRODUCT" to ASSERT.
As a result, function print_frames() is not used in optimized VM build.