Remove the prof_tctx_state_destroying transitory state and instead add
the tctx_uid field, so that the tuple <thr_uid, tctx_uid> uniquely
identifies a tctx. This assures that tctx's are well ordered even when
more than two with the same thr_uid coexist. A previous attempted fix
based on prof_tctx_state_destroying was only sufficient for protecting
against two coexisting tctx's, but it also introduced a new dumping
race.
These regressions were introduced by
602c8e0971160e4b85b08b16cf8a2375aa24bc04 (Implement per thread heap
profiling.) and 764b00023f2bc97f240c3a758ed23ce9c0ad8526 (Fix a heap
profiling regression.).
04211e2266