108486: configure.ac: add --enable-bogus-system-python

[Andrew Udvare]

https://gerrit.libreoffice.org/c/core/+/108486

Hi all,

My change is to allow macOS users to pick their own Python version for Pyuno. This is mostly intended for the MacPorts build but it can be applied to any user on macOS wanting to build the source to use with their own version of Python. The new option --enable-bogus-system-python is marked as not recommended to signal that this is not typically used. Unlike the bogus-pkg-config check, it does not test whether the Python version specified is actually 'bogus' (broken).

On macOS, /usr/bin/python3 can exist but without Xcode et al installed it is a stub. After Xcode et al is installed, it is a valid Python installation to build against. Note that MacPorts links against its own Python 3 implementation and not Apple's.

MacPorts port data: https://github.com/macports/macports-ports/tree/master/office/libreoffice (the webdav patch is already in https://gerrit.libreoffice.org/c/core/+/108262 )

We want to limit the amount of packages and duplicates of things like Python implementations. And as with all packages (ports) generally, our goal is to be able to build LibreOffice in the MacPorts environment without patches.

Thanks

-- 
Andrew Udvare