Use adviced c++ flag to supress warning on mingw

CMakeLists.txt

@@ -288,12 +288,11 @@ ELSEIF( CMAKE_COMPILER_IS_MINGW )
     message(WARNING "MinGW is old, if you experience errors, update MinGW.")
   ENDIF()
   IF(NOT ASSIMP_HUNTER_ENABLED)
-    SET(CMAKE_CXX_FLAGS "-std=c++11 ${CMAKE_CXX_FLAGS}")
+    SET(CMAKE_CXX_FLAGS "-std=gnu++11 ${CMAKE_CXX_FLAGS}")
     SET(CMAKE_C_FLAGS "-fPIC ${CMAKE_C_FLAGS}")
   ENDIF()
   SET(CMAKE_CXX_FLAGS "-fvisibility=hidden -fno-strict-aliasing -Wall -Wno-long-long -Wa,-mbig-obj -O3 ${CMAKE_CXX_FLAGS}")
   SET(CMAKE_C_FLAGS "-fno-strict-aliasing ${CMAKE_C_FLAGS}")
-  ADD_DEFINITIONS( -U__STRICT_ANSI__ )
 ENDIF()
 
 IF ( IOS AND NOT ASSIMP_HUNTER_ENABLED)