Drop Emacs versions that depend on obsolete gcc49Stdenv

[akirak]

See #311.

[akirak]

@purcell Emacs 25.3 fails to build on x86_64-darwin, and I don't know how to fix the issue, because I have no experience on Mac. Could you investigate the issue?

[purcell]

Emacs 25.3 fails to build on x86_64-darwin, and I don't know how to fix the issue, because I have no experience on Mac. Could you investigate the issue?

Fwiw, this actually runs okay for me on my ARM MacOS, but building as x86, just like in GitHub Actions:

nix --system x86_64-darwin run 'github:akirak/nix-emacs-ci/drop-gcc49-dependants#emacs-25-3' -- -Q

[akirak]

Cross-compiling the darwin package on my Linux (NixOS) machine fails:

nix --system x86_64-darwin build .#emacs-25-3 -L --show-trace

error: derivation '/nix/store/k8nlvr4idf52i4ilhvi6wzhn6mi7sfid-emacs-25-3.drv' requested impure path '/bin/sh', but it was not in allowed-impure-host-deps

nix --system x86_64-darwin build .#emacs-25-3 --option allowed-impure-host-deps /bin -L --show-trace

error: derivation '/nix/store/k8nlvr4idf52i4ilhvi6wzhn6mi7sfid-emacs-25-3.drv' requested impure path '/usr/lib/libSystem.B.dylib', but it was not in allowed-impure-host-deps

The error is specific to cross-compilation, so I don't find the issue fatal.

[akirak]

Closing in favour of #315