Fix a heap profiling regression.

Add the prof_tctx_state_destroying transitionary state to fix a race
between a thread destroying a tctx and another thread creating a new
equivalent tctx.

This regression was introduced by
602c8e0971 (Implement per thread heap
profiling.).

include/jemalloc/internal/prof.h

@@ -81,6 +81,7 @@ struct prof_cnt_s {
 typedef enum {
 	prof_tctx_state_initializing,
 	prof_tctx_state_nominal,
+	prof_tctx_state_destroying,
 	prof_tctx_state_dumping,
 	prof_tctx_state_purgatory /* Dumper must finish destroying. */
 } prof_tctx_state_t;