expat: Fix cmake config files

Header & library path constructions in CMake modules expect them to reside under the same prefix as the CMake files.
This assumption doesn't work with our multiple outputs so we patch the library path to the correct output.

Co-authored-by: Dmitry Kalinkin <dmitry.kalinkin@gmail.com>

pkgs/development/libraries/expat/default.nix

@@ -27,6 +27,13 @@ stdenv.mkDerivation rec {
     patchShebangs ./configure ./run.sh ./test-driver-wrapper.sh
   '';
 
+  # CMake files incorrectly calculate library path from dev prefix
+  # https://github.com/libexpat/libexpat/issues/501
+  postFixup = ''
+    substituteInPlace $dev/lib/cmake/expat-${version}/expat-noconfig.cmake \
+      --replace "$"'{_IMPORT_PREFIX}' $out
+  '';
+
   meta = with lib; {
     homepage = "https://libexpat.github.io/";
     description = "A stream-oriented XML parser library written in C";