msmtp: Configure sysconfdir to point to /etc

[kampka]

Motivation for this change

The current build lets the SYSCONFDIR of msmtp point to the nix store /nix/.../msmtp-1.81/etc, which is not very useful.
This change will allow for system wide configuration to be placed in /etc instead.

I only tested this one using an overlay because I believe it to be trivial, can do more tests if requested.

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)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

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[peterhoeg]

And make install doesn't try to put something in there?

[kampka]

msmtp does not ship a default config or something that would be put there if that is what you are asking about, so no, nothing is installed into /etc, the path is just compiled into the binary.

[hedning]

This is a nit pick, but it's good to suffix commit messages with the package attribute path, ie. mstmp: in this case.

[kampka]

@hedning valid point, fixed

[hedning]

@GrahamcOfBorg build msmtp

[hedning]

--sysconfdir=/etc seems like a common pattern 👍

[peterhoeg]

--sysconfdir=/etc seems like a common pattern

It blows up spectacularly if the installPhase tries to put something in there of course which is the reason it's not part of the standard builder.