eagle: 7.5 -> 7.7

This is the latest release from Cadsoft, before they were bought by
Autocad. Autocad has released 8.x, but

- it requires reworking the Nix expression (different packaging)
- the paid license version requires a monthly subscription fee, you never
  "own" the software (AFAICT).

Due to the licensing change in 8.x, I think keeping Eagle 7.x around is
a good idea.