graphite2: point to correct includedir in the .pc file

The CMakeLists.txt assumes that the include headers will end up in the
same directory as the lib files. This is not the case in this derivation
since we separate out from dev making the emitted .pc file reference
nonexisting directory.

pkgs/development/libraries/silgraphite/graphite2.nix

@@ -48,6 +48,10 @@ stdenv.mkDerivation (finalAttrs: {
     # support cross-compilation by using target readelf binary:
     substituteInPlace Graphite.cmake \
       --replace 'readelf' "${stdenv.cc.targetPrefix}readelf"
+
+    # headers are located in the dev output:
+    substituteInPlace CMakeLists.txt \
+      --replace-fail ' ''${CMAKE_INSTALL_PREFIX}/include' " ${placeholder "dev"}/include"
   '';
 
   cmakeFlags = lib.optionals static [