Meson 0.56.2 and Python39 --> dav1d failing

[Ken Cunningham]

That was a very nice fix...good to see how to do it properly now and then!

K

> On Feb 3, 2021, at 6:24 AM, Joshua Root <jmr at macports.org> wrote:
> 
> On 2021-2-3 23:49 , Ken Cunningham wrote:
>> dav1d is failing on 10.7 and 10.8 on the configure test for atomic.
>> it's building on 10.6 with clang 9.0, so probably needs to blacklist clangs older than 10.9's clang.
>> nothing to do with meson, looks to me...
> 
> It's claimed to be written in C99, but requires either C11's stdatomic.h or GCC extensions. Hmmm.
> 
> - Josh