Fix target definition for older CMake versions

Author: rickertm

cmake/FindIconv.cmake

@@ -76,7 +76,11 @@ else()
 endif()
 
 if(Iconv_FOUND AND NOT TARGET Iconv::Iconv)
-	add_library(Iconv::Iconv INTERFACE IMPORTED)
+	if(Iconv_IS_BUILT_IN)
+		add_library(Iconv::Iconv INTERFACE IMPORTED)
+	else()
+		add_library(Iconv::Iconv UNKNOWN IMPORTED)
+	endif()
 	if(NOT Iconv_IS_BUILT_IN AND Iconv_LIBRARY_RELEASE)
 		set_property(TARGET Iconv::Iconv APPEND PROPERTY IMPORTED_CONFIGURATIONS RELEASE)
 		set_target_properties(Iconv::Iconv PROPERTIES IMPORTED_LOCATION_RELEASE "${Iconv_LIBRARY_RELEASE}")