fetchgitlocal: local fetcher based on git ls-files

pkgs/build-support/fetchgitlocal/default.nix

@@ -0,0 +1,10 @@
+{ runCommand, git }: src:
+
+runCommand "local-git-export" {} ''
+  cd ${src}
+  mkdir -p "$out"
+  for file in $(${git}/bin/git ls-files); do
+    mkdir -p "$out/$(dirname $file)"
+    cp -d $file "$out/$file"
+  done
+''