add warning when building against FLTK 1.4

Author: MoAlyousef

CMakeLists.txt

@@ -97,8 +97,9 @@ if (ENABLE_FLTK_1_4)
         )
         FetchContent_MakeAvailable(FLTK)
         find_package(FLTK 1.4 CONFIG REQUIRED)
-        list(APPEND DILLO_FLTK_LIBS fltk::fltk)
     endif()
+    message(WARNING "Dillo will attempt to link against FLTK 1.4. This might cause rendering issues!")
+    list(APPEND DILLO_FLTK_LIBS fltk::fltk)
 else()
     find_package(FLTK REQUIRED) # 1.3
     list(APPEND DILLO_FLTK_INCLUDE_DIR ${FLTK_INCLUDE_DIR})