[OMPT] Set thread_num in ompt_get_task_info()

[sconvent]

Summary

thread_num was not set until now.
I will update the task_types.c testcase to also test ompt_get_task_info(), including thread_num.

[Hahnfeld]

IMO this should be merged with D42472: It fixes a function and needs a test, no need for two changes.

runtime/src/ompt-specific.cpp

if (thr) {
     }
     if (task_frame) {
       // OpenMP spec asks for the scheduling task to be returned.
       *task_frame = info ? &info->frame : NULL;
     }
     if (parallel_data) {
       *parallel_data = team_info ? &(team_info->parallel_data) : NULL;
     }
+    if (thread_num) {
+      *thread_num = __kmp_get_gtid();
+    }
     return info ? 2 : 0;
   }
   return 0;
 }
 
 //----------------------------------------------------------
 // team support
 //----------------------------------------------------------