Switch to our own mirror of libisl plus `ct-ng oldconfig` fixes#89599

Merged

bors merged 2 commits intorust-lang:masterfrom

rusticstuff:ci-fix

Oct 6, 2021

Commits on Oct 6, 2021

Switch to our own mirror of libisl
Mark-Simulacrum
committed
Get rid of broken `ct-ng oldconfig` everywhere and directly provide a suitable .config file.
hkratz
committed