Shiboken produces non-deterministic bindings

Two Shiboken wrappers built from the same source are incompatible with each other. A trivial reproduction of this is to build PySide twice and compare the pyside2_qtcore_python.h header files (example attached). This is makes it so that a client can't replace the build of PySide we shipped with their own. An example of the incompatibility is that the trivial conversion str<->unicode will fail.

TypeError: # 'MyQDialog.MyQDialog' called with wrong argument types:
# MyQDialog.MyQDialog(str, str, str, str, PySide2.QtWidgets.QWidget)
# Supported signatures:
MyQDialog.MyQDialog(unicode, unicode, unicode, unicode, PySide2.QtWidgets.QWidget = None)