Ubuntu – How to build `ungoogled-chromium` from source on Ubuntu 18.04

I've put in about an hour at this point, and I'm starting to feel a bit dead inside.

I started by downloading ungoogled-chromium version 71.0.3578.98-2 from GitHub. I extracted the tar.gz file into my home folder. Then, using the instructions from the "Any Linux Distribution" section of the build instructions. I followed the instructions to the point of adding the LLVM APT repo. I added the specified lines for Bionic (18.04) to my /etc/apt/sources.list file, retrieved the key with:

wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key|sudo apt-key add -
sudo apt-get update

This output these errors which look like this:

E: The repository 'https:/dl.winehq.org/wine-builds/ubuntu bionic Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: http://apt.llvm.org/bionic llvm-toolchain-bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 15CF4D18AF4F7421

I then, (though I knew it wouldn't work), ran:

sudo apt-get install clang-8 lld-8 llvm-8-dev python python3 ninja-build

and all of the LLVM packages were not able to be installed.

This is my first experience building from source, so I know inevitably made some obnoxious novice mistake.