better overriding of conf dir

confdir.patch

@@ -1,13 +0,0 @@
-diff --git a/meson.build b/meson.build
-index acaa39f764..b4efc581dc 100644
---- a/meson.build
-+++ b/meson.build
-@@ -1625,7 +1625,7 @@ sys.stdout.write(features)
- '''
- feature_str = run_command(python, '-c', feature_sort, feature_keys, check: true).stdout()
- conf_data.set_quoted('FULLCONFIG', feature_str)
--conf_data.set_quoted('MPV_CONFDIR', join_paths(get_option('prefix'), get_option('sysconfdir'), 'mpv'))
-+conf_data.set_quoted('MPV_CONFDIR', '/etc/mpv')
- configure_file(output : 'config.h', configuration : conf_data)
- message('List of enabled features: ' + feature_str)
- 

flake.nix

@@ -48,8 +48,8 @@
         newScripts = packages.packages.${prev.system};
       in rec {
         mpv-unwrapped = prev.mpv-unwrapped.overrideAttrs (oldAttrs: {
-          patches = (oldAttrs.patches or []) ++ [
-            ./confdir.patch
+          wafConfigureFlags = oldAttrs.wafConfigureFlags ++ [
+            "--confloaddir=/etc/mpv"
           ];
         });
         mpv = prev.wrapMpv mpv-unwrapped {