Meson 0.56.2 and Python39 --> dav1d failing

[Craig Treleaven]

> On Feb 3, 2021, at 10:01 PM, Joshua Root <jmr at macports.org> wrote:
> 
> On 2021-2-4 12:19 , Ken Cunningham wrote:
>>> On Feb 3, 2021, at 11:49 AM, Craig Treleaven <ctreleaven at macports.org> wrote:
>>> 
>>> But configure still failed on 10.7 and 10.8:
>> Oh no! It looked so great! I was really learning some things there. Perhaps it can be tweaked still.
>> If not, I guess we can still use the compiler_blacklist_versions approach and blacklist all the clangs < whatever 10.10 comes with.
> 
> Well now I'm just confused, because the test program builds fine on 10.7 outside of meson. Need to see the meson-log.txt.
> 
> - Josh

meson-log.txt from a failed configure on a 10.7 VM is at:

https://paste.macports.org/52ea26dc0724

In this case, clang clang-600.0.57 on 10.7 seems to be choking on "-Werror=ignored-optimization-argument”.  I don’t have 10.8 or 10.9 VM’s running at the moment but would suspect that they have the same problem.  Please recall that dav1d used to build OK on these systems before meson was updated to 0.56.2.

One of the devs on the dav1d project spotted that there was a recent commit to meson that appears to be the cause of this dav1d build problem:

https://github.com/mesonbuild/meson/blob/cd94cf8995bcddc40e627e94037e549b7a18b20e/mesonbuild/compilers/mixins/clang.py#L87

This resulted from a commit on Oct. 4, 2020:

https://github.com/mesonbuild/meson/commit/cd59ce98dc88318c6784cfddfe3fadda2495041b

This stuff is all well above my pay grade but it looks to me that it would likely break our builds on older OS X versions for other ports using meson.  Should we reverse this commit in our meson and file a bug upstream?

Craig