Claude review: kunit: Add backtrace suppression self-tests

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Asymmetric skip conditions between WARN_ON direct and indirect tests**

```c
+static void backtrace_suppression_test_warn_on_direct(struct kunit *test)
+{
+	if (!IS_ENABLED(CONFIG_DEBUG_BUGVERBOSE) && !IS_ENABLED(CONFIG_KALLSYMS))
+		kunit_skip(test, "requires CONFIG_DEBUG_BUGVERBOSE or CONFIG_KALLSYMS");
```

vs.

```c
+static void backtrace_suppression_test_warn_on_indirect(struct kunit *test)
+{
+	if (!IS_ENABLED(CONFIG_DEBUG_BUGVERBOSE))
+		kunit_skip(test, "requires CONFIG_DEBUG_BUGVERBOSE");
```

The direct test accepts either `CONFIG_DEBUG_BUGVERBOSE` or `CONFIG_KALLSYMS`, while the indirect test requires `CONFIG_DEBUG_BUGVERBOSE` only. There's no comment explaining why `CONFIG_KALLSYMS` is sufficient for the direct case but not the indirect case. A brief comment would help future readers understand the distinction.

**No test for allocation failure path**

There's no test that exercises the case where `__kunit_start_suppress_warning()` returns NULL (allocation failure). While hard to trigger in practice, it would verify the NULL-safety of the END/COUNT macros.

**Test coverage is otherwise solid**

The five test cases (WARN direct/indirect, WARN_ON direct/indirect, multi-warning) cover the key scenarios well.

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Generated by Claude Code Patch Reviewer