fbcode_builder: update FBPythonBinary.cmake to work on Windows
fbcode_builder: update FBPythonBinary.cmake to work on Windows

Summary:
On Windows we have to explicitly invoke `make_fbpy_archive.py` with python.
Therefore use CMake's built-in `FindPythonInterp` module to find the python
executable and use that when invoking `make_fbpy_archive.py`

This is slightly complicated by the effort required to find python with older
versions of CMake.  We ideally still want to support versions of CMake back to
at least 3.8, which means we need to still support finding Python with the
older `FindPythonInterp.cmake` module

Reviewed By: wez

Differential Revision: D17128606

fbshipit-source-id: 3f4beff76848b8a362ebdf21198e7a8bf1b0537f

facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst