What user account should this be installed under? I’m normally logged in as root (which there are legitimate arguments against). Your binaries got installed in /root/.cargo/bin. Not only was it not in the path, even after a reboot, but things in /root are off-limits to any other users, and some processes if they drop privileges. So I copied your binaries to /usr/bin or someplace in the path. Rustc worked.
Then I went back to trying to build Firefox 61.0 and it bombed with:
7:05.54 cargo:rerun-if-changed=/usr/src/misc/firefox/firefox-61.0/obj-aarch64-unknown-linux-gnu/dist/include/mozilla/intl/LineBreaker.h 7:05.54 cargo:rerun-if-changed=/usr/src/misc/firefox/firefox-61.0/obj-aarch64-unknown-linux-gnu/dist/include/mozilla/intl/WordBreaker.h 7:05.55 cargo:rerun-if-changed=/usr/src/misc/firefox/firefox-61.0/obj-aarch64-unknown-linux-gnu/dist/include/mozilla/RangeBoundary.h 7:05.55 cargo:rerun-if-changed=/usr/src/misc/firefox/firefox-61.0/obj-aarch64-unknown-linux-gnu/dist/include/nsRFPService.h 7:05.55 cargo:rerun-if-changed=/usr/src/misc/firefox/firefox-61.0/obj-aarch64-unknown-linux-gnu/dist/include/nsMediaFeatures.h 7:05.55 --- stderr 7:05.56 /usr/src/misc/firefox/firefox-61.0/obj-aarch64-unknown-linux-gnu/dist/include/mozilla/Compiler.h:49:12: fatal error: 'cstddef' file not found 7:05.56 /usr/src/misc/firefox/firefox-61.0/obj-aarch64-unknown-linux-gnu/dist/include/mozilla/Compiler.h:49:12: fatal error: 'cstddef' file not found, err: true
Which seems to be a rust problem I think. So I was thinking copying the binaries probably wasn’t good enough. So I did rustup self uninstall, deleted the copied binaries, logged in as a different user. Rebooted, rustc isn’t in the path.
Googling the error I get some hits in the Mozilla dev stuff about this error message being related to rust but nothing terribly conclusive. Running Debian Buster, installed Rust by fetching the installer with Curl, used the defaults.
Locate shows I have cstddef at: