Update CMakeLists.txt

Put it into the win32 for VS part.

CMakeLists.txt

@@ -173,7 +173,6 @@ SET (ASSIMP_VERSION ${ASSIMP_VERSION_MAJOR}.${ASSIMP_VERSION_MINOR}.${ASSIMP_VER
 SET (ASSIMP_SOVERSION 5)
 
 SET( ASSIMP_PACKAGE_VERSION "0" CACHE STRING "the package-specific version used for uploading the sources" )
-set(CMAKE_CXX_FLAGS_DEBUG "/D_DEBUG /MDd /Ob2")
 if(NOT HUNTER_ENABLED)
   # Enable C++11 support globally
   set_property( GLOBAL PROPERTY CXX_STANDARD 11 )
@@ -254,6 +253,7 @@ ELSEIF(MSVC)
   IF(MSVC12)
     ADD_COMPILE_OPTIONS(/wd4351)
   ENDIF()
+  SET(CMAKE_CXX_FLAGS_DEBUG "/D_DEBUG /MDd /Ob2")
 ELSEIF ( "${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" )
   IF(NOT HUNTER_ENABLED)
     SET(CMAKE_CXX_FLAGS "-fPIC -std=c++11 ${CMAKE_CXX_FLAGS}")