I tried to modify our thirdparty/src/dav1d-0.5.1.patch so it will build static version of new libdav1d library (I think ffmpeg.git dropped support for pre-1.0 versions of dav1d).
need nasm 2.14+
I build it on Slackware15.0 i586 with gcc11.2.0 and nasm 2.15.05 (there was some problem with multiple definitions in shared library, but we do not use it, so I just commented out linking it)
orig file:
Notably I can't see 0.5.1 there (probably still exist on videoLAN site somewhere?)