libavif: fix cmake files

pkgs/by-name/li/libavif/package.nix

@@ -98,7 +98,6 @@ stdenv.mkDerivation rec {
       GDK_PIXBUF_MODULEDIR=${gdkPixbufModuleDir} \
       GDK_PIXBUF_MODULE_FILE=${gdkPixbufModuleFile} \
       gdk-pixbuf-query-loaders --update-cache
-
     ''
     # Cross-compiled gdk-pixbuf doesn't support thumbnailers
     + lib.optionalString (stdenv.hostPlatform == stdenv.buildPlatform) ''
@@ -107,6 +106,11 @@ stdenv.mkDerivation rec {
         --set GDK_PIXBUF_MODULE_FILE ${gdkPixbufModuleFile}
     '';
 
+  postFixup = ''
+    substituteInPlace $dev/lib/cmake/libavif/libavif-config.cmake \
+      --replace-fail "_IMPORT_PREFIX \"$out\"" "_IMPORT_PREFIX \"$dev\""
+  '';
+
   meta = {
     description = "C implementation of the AV1 Image File Format";
     longDescription = ''