libkeyfinder: fix paths in pkg-config file

pkgs/development/libraries/audio/libkeyfinder/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchFromGitHub, cmake, fftw, catch2 }:
+{ lib, stdenv, fetchpatch, fetchFromGitHub, cmake, fftw, catch2 }:
 
 stdenv.mkDerivation rec {
   pname = "libkeyfinder";
@@ -11,6 +11,15 @@ stdenv.mkDerivation rec {
     sha256 = "sha256-7w/Wc9ncLinbnM2q3yv5DBtFoJFAM2e9xAUTsqvE9mg=";
   };
 
+  # in main post 2.2.6, see https://github.com/mixxxdj/libkeyfinder/issues/21
+  patches = [
+    (fetchpatch {
+      name = "fix-pkg-config";
+      url = "https://github.com/mixxxdj/libkeyfinder/commit/4e1a5022d4c91e3ecfe9be5c3ac7cc488093bd2e.patch";
+      sha256 = "08llmgp6r11bq5s820j3fs9bgriaibkhq8r3v2av064w66mwp48x";
+    })
+  ];
+
   nativeBuildInputs = [ cmake ];
 
   buildInputs = [ fftw ];