Use system-wide copy of expected-lite

--- cppgir-960fe054ffaab7cf55722fea6094c56a8ee8f18e.orig/CMakeLists.txt
+++ cppgir-960fe054ffaab7cf55722fea6094c56a8ee8f18e/CMakeLists.txt
@@ -76,14 +76,8 @@
     "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/${PROJECT_NAME}/override>"
 )
 
-set(EXPECTED_LITE_INCLUDE "expected-lite/include")
-if (EXISTS ${CMAKE_CURRENT_LIST_DIR}/${EXPECTED_LITE_INCLUDE}/nonstd/expected.hpp)
-    target_include_directories(gi INTERFACE
-        "$<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/${EXPECTED_LITE_INCLUDE}>"
-    )
-else ()
-    message (FATAL_ERROR "missing submodule expected-lite")
-endif ()
+find_package(expected-lite REQUIRED)
+target_link_libraries(gi INTERFACE nonstd::expected-lite)
 
 include(FindPkgConfig)
 pkg_check_modules(GOBJECT gobject-2.0)
@@ -241,8 +235,6 @@
 # headers
 install(DIRECTORY gi override
     DESTINATION ${CMAKE_INSTALL_FULL_INCLUDEDIR}/${PROJECT_NAME})
-install(DIRECTORY ${EXPECTED_LITE_INCLUDE}/nonstd
-    DESTINATION ${CMAKE_INSTALL_FULL_INCLUDEDIR}/${PROJECT_NAME}/gi)
 
 # doc
 install(FILES README.md docs/cppgir.md
--- cppgir-960fe054ffaab7cf55722fea6094c56a8ee8f18e.orig/cmake/cppgir-config.cmake
+++ cppgir-960fe054ffaab7cf55722fea6094c56a8ee8f18e/cmake/cppgir-config.cmake
@@ -1 +1,4 @@
+include(CMakeFindDependencyMacro)
+find_dependency(expected-lite)
+
 include("${CMAKE_CURRENT_LIST_DIR}/cppgir-targets.cmake")