Update LVGL to v9.1.0

lib/lvgl/CMakeLists.txt

@@ -1,7 +1,9 @@
 cmake_minimum_required(VERSION 3.12.4)
 
+set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)
+
 if(NOT ESP_PLATFORM)
-  project(lvgl HOMEPAGE_URL https://github.com/lvgl/lvgl)
+  project(lvgl LANGUAGES C CXX ASM HOMEPAGE_URL https://github.com/lvgl/lvgl)
 endif()
 
 set(LVGL_ROOT_DIR ${CMAKE_CURRENT_LIST_DIR})
@@ -15,3 +17,20 @@ elseif(MICROPY_DIR)
 else()
   include(${CMAKE_CURRENT_LIST_DIR}/env_support/cmake/custom.cmake)
 endif()
+
+#[[
+    unfortunately CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS does not work for global data. 
+    for global data we still need decl specs.
+    Check out the docs to learn more about the limitations of CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS
+    https://cmake.org/cmake/help/latest/prop_tgt/WINDOWS_EXPORT_ALL_SYMBOLS.html#prop_tgt:WINDOWS_EXPORT_ALL_SYMBOLS
+
+    For all compiled sources within the library (i.e. basically all lvgl files) we need to use dllexport.
+    For all compiled sources from outside the library (i.e. files which include lvgl headers) we need to use dllimport.
+    We can do this by using CMakes INTERFACE and PRIVATE keyword.
+  ]]
+if (MSVC)
+  target_compile_definitions(lvgl
+    INTERFACE LV_ATTRIBUTE_EXTERN_DATA=__declspec\(dllimport\)
+    PRIVATE LV_ATTRIBUTE_EXTERN_DATA=__declspec\(dllexport\)
+  )
+endif()