[lldb] Fix racing issue when loading inlined symbols from crash report

Following abba5de7, some tests started failing on green-dragon:

https://green.lab.llvm.org/green/job/lldb-cmake/55460/console



Looking at the backtrace, there seems to be a racing issue when deleting
the temporary directory containing all the JSON object files:

```
Traceback (most recent call last):
  File "/Users/buildslave/jenkins/workspace/lldb-cmake/lldb-build/lib/python3.10/site-packages/lldb/macosx/crashlog.py", line 1115, in __call__
    SymbolicateCrashLogs(debugger, shlex.split(command), result)
  File "/Users/buildslave/jenkins/workspace/lldb-cmake/lldb-build/lib/python3.10/site-packages/lldb/macosx/crashlog.py", line 1457, in SymbolicateCrashLogs
    SymbolicateCrashLog(crash_log, options)
  File "/Users/buildslave/jenkins/workspace/lldb-cmake/lldb-build/lib/python3.10/site-packages/lldb/macosx/crashlog.py", line 1158, in SymbolicateCrashLog
    with tempfile.TemporaryDirectory() as obj_dir:
  File "/usr/local/opt/python@3.10/Frameworks/Python.framework/Versions/3.10/lib/python3.10/tempfile.py", line 869, in __exit__
    self.cleanup()
  File "/usr/local/opt/python@3.10/Frameworks/Python.framework/Versions/3.10/lib/python3.10/tempfile.py", line 873, in cleanup
    self._rmtree(self.name, ignore_errors=self._ignore_cleanup_errors)
  File "/usr/local/opt/python@3.10/Frameworks/Python.framework/Versions/3.10/lib/python3.10/tempfile.py", line 855, in _rmtree
    _shutil.rmtree(name, onerror=onerror)
  File "/usr/local/opt/python@3.10/Frameworks/Python.framework/Versions/3.10/lib/python3.10/shutil.py", line 731, in rmtree
    onerror(os.rmdir, path, sys.exc_info())
  File "/usr/local/opt/python@3.10/Frameworks/Python.framework/Versions/3.10/lib/python3.10/shutil.py", line 729, in rmtree
    os.rmdir(path)
OSError: [Errno 66] Directory not empty: '/var/folders/09/r4vw4v8n5kb67jl66zvlbljw0000gn/T/tmp6qfifxk7'
```

This patch should fix that issue since it won't delete the object file
directory until we're sure that the modules adding tasks completed.

Signed-off-by: Med Ismail Bennani <ismail@bennani.ma>