[DynInst_API:] [dyninst/dyninst] 4fca3d: Fix compilation of thread_db_process (#571)

[Sasha NÃcolas <noreply@xxxxxxxxxx>]

  Branch: refs/heads/master
  Home:   https://github.com/dyninst/dyninst
  Commit: 4fca3d7ec39175f4afcca382dba60e4bd7346fbe
      https://github.com/dyninst/dyninst/commit/4fca3d7ec39175f4afcca382dba60e4bd7346fbe
  Author: Sasha NÃcolas <sasha@xxxxxxxxxxx>
  Date:   2019-05-08 (Wed, 08 May 2019)

  Changed paths:
    M proccontrol/src/int_thread_db.C
    M proccontrol/src/int_thread_db.h

  Log Message:
  -----------
  Fix compilation of thread_db_process (#571)

On a machine without libthread_db.so, the placeholder class had missing member functions and the contructors were calling wrong base constructors.