opendht: fix paths in pkg-config file

pkgs/development/libraries/opendht/default.nix

···
     "-DOPENDHT_PUSH_NOTIFICATIONS=ON"
   ];
 
+  # https://github.com/savoirfairelinux/opendht/issues/612
+  postPatch = ''
+    substituteInPlace CMakeLists.txt \
+      --replace '\$'{exec_prefix}/'$'{CMAKE_INSTALL_LIBDIR} '$'{CMAKE_INSTALL_FULL_LIBDIR} \
+      --replace '\$'{prefix}/'$'{CMAKE_INSTALL_INCLUDEDIR} '$'{CMAKE_INSTALL_FULL_INCLUDEDIR}
+  '';
+
   outputs = [ "out" "lib" "dev" "man" ];
 
   meta = with lib; {