hashmap: avoid using TLS in a destructor

Using C11 thread-local storage in destructors causes uninitialized
read. Let's avoid that using a direct comparison instead of using
the cached values. As this code path is taken only when compiled
with -DVALGRIND=1, the performance cost shouldn't matter too much.

Fixes #12814

(cherry picked from commit 31c9d74d)
(cherry picked from commit ffa47f67)