Ensure that CINDEX_VERSION_MINOR is never increased and that instead
specific macros indicate backported functionality. This minimizes
potential build problems with other API functions that might have been
backported or not in the meanwhile.
Change-Id: I44d868e82dd6a3ea5aa3e8b22e18bba5c4bf8d16
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>