Add PNG::PNG ALIAS target

Author: ruslo

cmake/Config.cmake.in

@@ -3,3 +3,12 @@ include(CMakeFindDependencyMacro)
 find_dependency(ZLIB CONFIG)
 
 include("${CMAKE_CURRENT_LIST_DIR}/@targets_export_name@.cmake")
+
+if(NOT TARGET PNG::PNG)
+  set_target_properties(
+      PNG::png
+      PROPERTIES
+      IMPORTED_GLOBAL True
+  )
+  add_library(PNG::PNG ALIAS PNG::png)
+endif()