Update CMakeLists.txt

- closes https://github.com/assimp/assimp/issues/2785
- Disable optimization in debug mode.

CMakeLists.txt

@@ -253,7 +253,7 @@ ELSEIF(MSVC)
   IF(MSVC12)
     ADD_COMPILE_OPTIONS(/wd4351)
   ENDIF()
-  SET(CMAKE_CXX_FLAGS_DEBUG "/D_DEBUG /MDd /Ob2 /Zi")
+  SET(CMAKE_CXX_FLAGS_DEBUG "/D_DEBUG /MDd /Ob2 /Zi /O0")
 ELSEIF ( "${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" )
   IF(NOT HUNTER_ENABLED)
     SET(CMAKE_CXX_FLAGS "-fPIC -std=c++11 ${CMAKE_CXX_FLAGS}")