Python: stub out python GIL calls if no thread support
Python: stub out python GIL calls if no thread support

This resolves linking errors when doing static cross-compile builds
against python with no thread support.

SimVascular/VTK,sumedhasingla/VTK,keithroe/vtkoptix,sumedhasingla/VTK,keithroe/vtkoptix,SimVascular/VTK,SimVascular/VTK,sumedhasingla/VTK,SimVascular/VTK,SimVascular/VTK,keithroe/vtkoptix,keithroe/vtkoptix,sumedhasingla/VTK,SimVascular/VTK,keithroe/vtkoptix,sumedhasingla/VTK,keithroe/vtkoptix,sumedhasingla/VTK,sumedhasingla/VTK,keithroe/vtkoptix,SimVascular/VTK,sumedhasingla/VTK,SimVascular/VTK,keithroe/vtkoptix