JPEG-XL and upgrading MinGW GCC

[L. E. Segovia]

Hi all,

I've been tinkering the past couple of days with JPEG-XL, getting it in 
place within 3rdparty. I found that one of the dependencies of libjxl is 
Google's Highway library, which requires something newer than GCC 7.3 
due to:

- support of AVX512 intrinsics
- usage of the __STDC_FORMAT_MACROS

Fixing the former is needed for our Windows CI, but it will still fail 
on the former item.

Questions:

- Do you know if the Docker image has been updated?

- And what can we do with our Windows build itself, which uses MinGW GCC 
7.3?  Obviously, switching to MSYS does the trick, but I think Dmitry's 
been reluctant in the past to just do the jump.

Cheers,

amyspark.

-- 
amyspark 🌸 https://www.amyspark.me