recoll: fix no/bad configuration error on darwin

Prior to this fix, running recoll fails with the following error:

No/bad main configuration file in /nix/store/.../Resources/examples.

The path is incorrect and RECOLL_DATADIR should be used.

pkgs/applications/search/recoll/default.nix

@@ -46,6 +46,13 @@ mkDerivation rec {
     ++ lib.optionals (!withGui) [ "--disable-qtgui" "--disable-x11mon" ]
     ++ (if stdenv.isLinux then [ "--with-inotify" ] else [ "--without-inotify" ]);
 
+  NIX_CFLAGS_COMPILE = [ "-DNIXPKGS" ];
+
+  patches = [
+    # fix "No/bad main configuration file" error
+    ./fix-datadir.patch
+  ];
+
   nativeBuildInputs = [
     file pkg-config python3Packages.setuptools which
   ];

pkgs/applications/search/recoll/fix-datadir.patch

@@ -0,0 +1,13 @@
+diff --git a/utils/rclutil.cpp b/utils/rclutil.cpp
+index 60ff5fb..4a59ccc 100644
+--- a/utils/rclutil.cpp
++++ b/utils/rclutil.cpp
+@@ -279,7 +279,7 @@ const string& path_pkgdatadir()
+         "a subfolder of the installation directory. \n"
+         "Please set the RECOLL_DATADIR environment variable to point to it\n"
+         "(e.g. setx RECOLL_DATADIR \"C:/Program Files (X86)/Recoll/Share)\"\n";
+-#elif defined(__APPLE__) && !defined(MACPORTS) && !defined(HOMEBREW)
++#elif defined(__APPLE__) && !defined(MACPORTS) && !defined(HOMEBREW) && !defined(NIXPKGS)
+     uint32_t size = 0;
+     _NSGetExecutablePath(nullptr, &size);
+     char *path= (char*)malloc(size+1);