Meson 0.56.2 and Python39 --> dav1d failing

[Ken Cunningham]

as meson was currently broken on older systems I pushed through a fix for this just now.

We can revise it to whatever upstream wants to do when they get around to it, if they want to do anything about it.

I took the opportunity to also add a cross file similar to the ones I added previously for i386 and x86_64, and this should allow cross building of meson ports on BigSur.

I deeply apologize — I stupidly made a tiny typo by leaving in a testing tweak, and only saw it when I looked at the commit afterwards to make sure it was all well. So I had to fix that quickly.

Normally I would have PR’d this, and waited for review but as in one case the systems were broken, and in the other it involved the cross-building I added, I went ahead with it.

My apologies if this is felt to break protocol; just trying to do the right thing here.

Bes;t

Ken


PS — any feedback on the success of the cross building, or any failures encountered, would be much appreciated.  I believe this is the only setup that currently allows meson cross building on BigSur that is available for macOS.