Allow the wrapper's preprocessor to perform macro expansion.  Prior
to this change, only a few function macros that were hard-coded into
the wrappers could be used in the VTK headers.  Custom macros would
previously cause the wrapper generation to fail.

Some macros are not expanded for the sake of backwards compatibility:
1) VTK_* macro constants are not expanded, since these are recognized
by some of the later stages of the wrapper processing.
2) vtkDataArray, if defined as a macro, is not expanded in order to
allow the vtkDataArrayTemplate superclass trick work as before.
3) All previously hard-coded macros such as the vtkSet/Get macros are
still hard-coded for now, to ensure backwards compatiblity

Change-Id: I96deec4b9c98badfed88831027011904d197840f