Revert "BUILD: Makefile: disable -Warray-bounds until it's fixed in gcc 11"

Revert "BUILD: Makefile: disable -Warray-bounds until it's fixed in gcc 11"

This reverts commit 5e8c35da1b93b64ec4892192aec3d61d73b3bbce.

While the issue is being discussed with gcc folks, a reasonable workaround
could be found for the tls_keys_ref list usage which doesn't significantly
complicate the code. Since it was the only place triggering the warning and
I don't feel very comfortable leaving this one disabled for too long, let's
re-enable it right now. This definitely closes issue #1010.