fix: update fixup phase for control-center (#25)

Fixes a build failure caused by the recently introduced noBrokenSymlinks
derivation check. The binary is now already being renamed in the
preFixup phase so the correct path can be symlinked by the
separateDebugInfo script.

Also fixes the substitution inside of desktop files which seems to
have been broken by an upstream update.

Author: brckd

pkgs/mithril-control-center/default.nix

@@ -7,11 +7,13 @@ gnome-control-center.overrideAttrs (old: {
 
   patches = old.patches ++ (readPatches ./.);
 
-  postFixup = ''
+  preFixup = ''
     for i in $out/share/applications/*; do
-      substituteInPlace $i --replace "Exec=$out/bin/gnome-control-center" "Exec=$out/bin/mithril-control-center"
+      substituteInPlace $i --replace-warn "Exec=gnome-control-center" "Exec=mithril-control-center"
     done
     mv $out/bin/gnome-control-center $out/bin/mithril-control-center
+
+    ${old.preFixup}
   '';
 
   doCheck = false;