The following changes have been made to this attribute with
WITH_PYTHON_MODULE is defined:
- Defaults to an empty string (instead of pointing to __init__.so).
- It's writable, so script authors can point to a valid Blender binary.
`where_am_i(..)` is no longer used by BKE_appdir_program_path_init,
there is now a separate code-path for setting the initial program
directory, calls after this can be used to set the binary path.
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