WIP Nix flake for building evm-llvm.
To build evm-llvm just run
nix build in the evm-llvm-nix directory
Since llvm is a very large build and since nix builds in TMPDIR by default, this can cause memory over-use problems in systems where /tmp is a tmpfs (like some linux distros).
To solve this, run:
TMPDIR=/var/tmp nix build
This tells nix to build in /var/tmp without actually changing the TMPDIR environment variable.