EmptyEpsilon: use python3

[dotlambda]

Motivation for this change

#18185

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Fits CONTRIBUTING.md.

---

cc @fpletz
Note that this was not tested.

[GrahamcOfBorg]

Success on aarch64-linux (full log)

Attempted: EmptyEpsilon

Partial log (click to expand)

-- Installing: /nix/store/bgg90r592j3idqc35zag93lqkgkh8q1d-empty-epsilon-2018.02.15/bin/EmptyEpsilon
-- Installing: /nix/store/bgg90r592j3idqc35zag93lqkgkh8q1d-empty-epsilon-2018.02.15/./script_reference.html
post-installation fixup
shrinking RPATHs of ELF executables and libraries in /nix/store/bgg90r592j3idqc35zag93lqkgkh8q1d-empty-epsilon-2018.02.15
shrinking /nix/store/bgg90r592j3idqc35zag93lqkgkh8q1d-empty-epsilon-2018.02.15/bin/EmptyEpsilon
strip is /nix/store/zrs21zqcchgyabjf4xfimncdq16njizc-binutils-2.30/bin/strip
stripping (with command strip and flags -S) in /nix/store/bgg90r592j3idqc35zag93lqkgkh8q1d-empty-epsilon-2018.02.15/bin
patching script interpreter paths in /nix/store/bgg90r592j3idqc35zag93lqkgkh8q1d-empty-epsilon-2018.02.15
checking for references to /build in /nix/store/bgg90r592j3idqc35zag93lqkgkh8q1d-empty-epsilon-2018.02.15...
/nix/store/bgg90r592j3idqc35zag93lqkgkh8q1d-empty-epsilon-2018.02.15

[GrahamcOfBorg]

Success on x86_64-linux (full log)

Attempted: EmptyEpsilon

Partial log (click to expand)

-- Installing: /nix/store/yjar1jr63spf4z0wa5liwxx8cqx51hy0-empty-epsilon-2018.02.15/bin/EmptyEpsilon
-- Installing: /nix/store/yjar1jr63spf4z0wa5liwxx8cqx51hy0-empty-epsilon-2018.02.15/./script_reference.html
post-installation fixup
shrinking RPATHs of ELF executables and libraries in /nix/store/yjar1jr63spf4z0wa5liwxx8cqx51hy0-empty-epsilon-2018.02.15
shrinking /nix/store/yjar1jr63spf4z0wa5liwxx8cqx51hy0-empty-epsilon-2018.02.15/bin/EmptyEpsilon
strip is /nix/store/1hi76hr87bd1y1q1qjk0lv8nmcjip1c8-binutils-2.30/bin/strip
stripping (with command strip and flags -S) in /nix/store/yjar1jr63spf4z0wa5liwxx8cqx51hy0-empty-epsilon-2018.02.15/bin
patching script interpreter paths in /nix/store/yjar1jr63spf4z0wa5liwxx8cqx51hy0-empty-epsilon-2018.02.15
checking for references to /build in /nix/store/yjar1jr63spf4z0wa5liwxx8cqx51hy0-empty-epsilon-2018.02.15...
/nix/store/yjar1jr63spf4z0wa5liwxx8cqx51hy0-empty-epsilon-2018.02.15

[infinisil]

Just did a quick test, seems to work fine