fetchFromGitiles: init

This has the same motivation as fetchFromGitHub/fetchFromGitLab --
it's cheaper to download a tarball of a single revision than it is to
download a whole history.

I could have gone with domain/group/repo, like fetchFromGitLab, but it
would have made implementation more difficult, and this syntax means
it's a drop-in replacement for fetchgit, so I decided it wasn't worth
it.

pkgs/build-support/fetchgitiles/default.nix

@@ -0,0 +1,10 @@
+{ fetchzip, lib }:
+
+{ url, rev, name ? "source", ... } @ args:
+
+fetchzip ({
+  inherit name;
+  url = "${url}/+archive/${rev}.tar.gz";
+  stripRoot = false;
+  meta.homepage = url;
+} // removeAttrs args [ "url" "rev" ]) // { inherit rev; }