mpc_cli: fix build with meson 0.60

Adds upstream patch from https://github.com/MusicPlayerDaemon/mpc/pull/76
to make the dependency on rsync optional.

pkgs/applications/audio/mpc/default.nix

@@ -1,6 +1,7 @@
 { lib
 , stdenv
 , fetchFromGitHub
+, fetchpatch
 , meson
 , ninja
 , pkg-config
@@ -20,6 +21,14 @@ stdenv.mkDerivation rec {
     sha256 = "sha256-2FjYBfak0IjibuU+CNQ0y9Ei8hTZhynS/BK2DNerhVw=";
   };
 
+  patches = [
+    # fix the build with meson 0.60 (https://github.com/MusicPlayerDaemon/mpc/pull/76)
+    (fetchpatch {
+      url = "https://github.com/MusicPlayerDaemon/mpc/commit/b656ca4b6c2a0d5b6cebd7f7daa679352f664e0e.patch";
+      sha256 = "sha256-fjjSlCKxgkz7Em08CaK7+JAzl8YTzLcpGGMz2HJlsVw=";
+    })
+  ];
+
   buildInputs = [ libmpdclient ] ++ lib.optionals stdenv.isDarwin [ libiconv ];
 
   nativeBuildInputs = [ meson ninja pkg-config sphinx ];