[OpenMP][stats] reset serial state when re-entering serial region

[jlpeyton]

Summary

Forgot to reset the stats state when re-entering serial region for both pragma omp parallel and pragma omp teams

[tlwilmar]

LGTM

openmp/runtime/src/kmp_csupport.cpp

#endif
                     );
 
     va_end(ap);
   }
 
 #if KMP_STATS_ENABLED
   if (previous_state == stats_state_e::SERIAL_REGION) {
     KMP_EXCHANGE_PARTITIONED_TIMER(OMP_serial);
+    KMP_SET_THREAD_STATE(previous_state);
   } else {
     KMP_POP_PARTITIONED_TIMER();
   }
 #endif // KMP_STATS_ENABLED
 }
 
 /*!
 @ingroup PARALLEL
#endif
 
   this_thr->th.th_teams_microtask = NULL;
   this_thr->th.th_teams_level = 0;
   *(kmp_int64 *)(&this_thr->th.th_teams_size) = 0L;
   va_end(ap);
 #if KMP_STATS_ENABLED
   if (previous_state == stats_state_e::SERIAL_REGION) {
     KMP_EXCHANGE_PARTITIONED_TIMER(OMP_serial);
+    KMP_SET_THREAD_STATE(previous_state);
   } else {
     KMP_POP_PARTITIONED_TIMER();
   }
 #endif // KMP_STATS_ENABLED
 }
 
 // I don't think this function should ever have been exported.
 // The __kmpc_ prefix was misapplied.  I'm fairly certain that no generated