The latest cmake-rs assumes cmake's --parallel works. That was added in
cmake 3.12, but a lot of our CI builds run on Ubuntu Bionic which only
has cmake 3.10.
Fixes#7927Closes#7952
Follow-up to 6d972c8b1c which missed updating this directory name.
Also no longer call it crustls in the docs and bump to rusttls-ffi 0.7.1
Closes#7311