Meson 0.56.2 and Python39

[Craig Treleaven]

Hi:

It might be that the meson update and/or the switch to python39 has broken builds on older Mac OS versions.  Specifically, I updated dav1d to 0.8.1 and it no longer configures successfully on 10.9 and older versions.  Upstream says that the now-failing configure test (a simple test to see if the compiler can create an executable) has not changed.  

Am I the only one seeing this?

The meson project doesn’t seem to have a change log and I haven’t waded through all of the commits between versions.  Is there a test suite with meson?  Have we checked it?  

Tomorrow, I think I’m going to try to bring up some VM’s and see if meson-log.txt has anything interesting on a failing OS version.

Craig