Fix pkgconfig includedirs

E.g. linux minizip can be located in /usr/include/minizip, which
requires adding the extra includedir from pkgconfig.

If pkgconfig defines an includedir for a module, it should be included.

CMake/DolphinLibraryTools.cmake

@@ -88,6 +88,9 @@ function(dolphin_find_optional_system_library_pkgconfig library search alias bun
     message(STATUS "Using system ${library}")
     dolphin_alias_library(${alias} PkgConfig::${library})
     set(${library}_TYPE "System" PARENT_SCOPE)
+    if(${${alias}_INCLUDEDIR})
+      include_directories("${${alias}_INCLUDEDIR}")
+    endif()
   else()
     dolphin_add_bundled_library(${library} ${bundled_path})
     set(${library}_TYPE "Bundled" PARENT_SCOPE)