3406. [bug] mem.c: Fix compilation errors when building with
ISC_MEM_TRACKLINES or ISC_MEMPOOL_NAMES disabled.
Also, ISC_MEM_DEBUG is no longer optional. [RT #31559]
(cherry picked from commit 2f57f353e8)
(cherry picked from commit 76e34eb2fd)
(cherry picked from commit 7c5941b4c2)