Fix problems with finding libexpat

fixes #9581
fixes #10390

CMakeLists.txt

@@ -465,10 +465,12 @@ find_package(EXPAT REQUIRED)
 
 add_library(libexpat INTERFACE)
 
-if (TARGET EXPAT::EXPAT )
+if (TARGET EXPAT::EXPAT ) # found by a newer Find script
     target_link_libraries(libexpat INTERFACE EXPAT::EXPAT)
-elseif(TARGET expat::expat)
+elseif(TARGET expat::expat) # found by a config script
     target_link_libraries(libexpat INTERFACE expat::expat)
+else() # found by an older Find script
+    target_link_libraries(libexpat INTERFACE ${EXPAT_LIBRARIES})
 endif ()
 
 find_package(PNG REQUIRED)

cmake/modules/FindEXPAT.cmake

@@ -1,36 +0,0 @@
-set(_q "")
-if(EXPAT_FIND_QUIETLY)
-    set(_q QUIET)
-endif()
-find_package(EXPAT ${EXPAT_FIND_VERSION} CONFIG ${_q})
-
-if(NOT EXPAT_FIND_QUIETLY)
-    if (NOT EXPAT_FOUND)
-        message(STATUS "Falling back to MODULE search for EXPAT...")
-    else()
-        message(STATUS "EXPAT found in ${EXPAT_DIR}")
-    endif()
-endif()
-
-if (NOT EXPAT_FOUND)
-    set(_modpath ${CMAKE_MODULE_PATH})
-    set(CMAKE_MODULE_PATH "")
-    include(FindEXPAT)
-    set(CMAKE_MODULE_PATH ${_modpath})
-
-    if (NOT TARGET EXPAT::EXPAT)
-        add_library(EXPAT::EXPAT INTERFACE)
-        target_link_libraries(EXPAT::EXPAT INTERFACE ${EXPAT_LIBRARIES})
-        target_include_directories(EXPAT::EXPAT INTERFACE ${EXPAT_INCLUDE_DIRS})
-    endif ()
-endif()
-
-if (EXPAT_FOUND AND NOT TARGET EXPAT::EXPAT)
-    add_library(libexpat INTERFACE)
-    add_library(EXPAT::EXPAT ALIAS libexpat)
-    target_link_libraries(libexpat INTERFACE expat::expat)
-    if (NOT EXPAT_LIBRARIES)
-        set(EXPAT_LIBRARIES expat::expat CACHE STRING "")
-    endif ()
-endif ()
-