fix(fuzzer): fix link failure, UBSan in fuzz targets, add ASan log capture

[jbachorik]

What does this PR do?:
Fixes two fuzz-CI failures found in run 27394653882 and adds ASan log capture to make future testAsan crashes diagnosable.

1. callTraceStorage.h — static const u64 DROPPED_TRACE_ID changed to static constexpr. The fuzz target passes it by const u64& to unordered_set::find, which ODR-uses it. static const (non-constexpr) requires an out-of-class definition in that case; static constexpr is implicitly inline in C++17 and needs none. The linker error was: undefined reference to CallTraceStorage::DROPPED_TRACE_ID.

2. buffers.h — Added __attribute__((no_sanitize("undefined"))) to put16. It does an unaligned short* store to a byte array (same pattern as put32, which already carries this annotation with a comment). UBSan reported: store to misaligned address for type 'short', which requires 2 byte alignment.

3. ConfigurationPresets.kt — Added log_path=/tmp/asan.log to ASAN_OPTIONS for the asan config. ASan writes one file per PID (/tmp/asan.log.<pid>), preserving output even when the JVM exits abruptly before Gradle captures stderr.

4. test_workflow.yml — Added Upload ASan logs artifact steps to all four test jobs (glibc/musl × amd64/aarch64), conditioned on failure() && matrix.config == 'asan' with if-no-files-found: ignore. This makes the actual ASan report available as a downloadable artifact on future testAsan failures.

Motivation:
The fuzz CI job was failing with a linker error (never ran the callTraceStorage fuzzer), and the buffers fuzzer was hitting a UBSan error. The testAsan job was crashing with exit code 1 and no visible output — the ASan report was being lost.

Additional Notes:
The testAsan crash root cause is still unknown — changes 3 and 4 are purely diagnostic. The next failure will produce an asan-logs-glibc-11-amd64 artifact with the actual report.

How to test the change?:

• CI: the fuzz job should now link and run both fuzz targets without UBSan errors.
• CI: on any future testAsan failure, an asan-logs-* artifact will appear in the run.

For Datadog employees:

• This PR doesn't touch any of that.
• JIRA: [JIRA-XXXX]

[dd-octo-sts]

CI Test Results

Run: #27423686995 | Commit: ca0c64e | Duration: 13m 15s (longest job)

✅ All 32 test jobs passed

Status Overview

JDK	glibc-aarch64/debug	glibc-amd64/debug	musl-aarch64/debug	musl-amd64/debug
8	-	✅	-	-
8-ibm	-	✅	-	-
8-j9	✅	✅	-	-
8-librca	-	-	✅	✅
8-orcl	-	✅	-	-
11	-	✅	-	-
11-j9	✅	✅	-	-
11-librca	-	-	✅	✅
17	✅	✅	-	-
17-graal	✅	✅	-	-
17-j9	✅	✅	-	-
17-librca	-	-	✅	✅
21	✅	✅	-	-
21-graal	✅	✅	-	-
21-librca	-	-	✅	✅
25	✅	✅	-	-
25-graal	✅	✅	-	-
25-librca	-	-	✅	✅

Legend: ✅ passed | ❌ failed | ⚪ skipped | 🚫 cancelled

Summary: Total: 32 | Passed: 32 | Failed: 0

---

Updated: 2026-06-12 15:13:33 UTC