When a btuwi pair is freed, put the freed memory on the free list associated with the appropriate unwinder, and not always on the free list for unwinder 0.
When a btuwi pair is freed, put the freed memory on the free list associated
with the appropriate unwinder, and not always on the free list for unwinder 0.

HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit