Avoid override warnings in haxe 4

Older versions of haxe do not generate overrides so they will keep
showing warnings. By omitting any overrides, we prevent these warnings
from showing up.

Author: tobil4sk

include/hx/StringAlloc.h

@@ -17,7 +17,7 @@ class IStringAlloc
 };
 
 #ifndef HXCPP_OVERRIDE
-   #if __cplusplus >= 201103L || (defined(_MSC_VER) && _MSVC_LANG >= 201103L)
+   #if HXCPP_API_LEVEL >= 500 && (__cplusplus >= 201103L || (defined(_MSC_VER) && _MSVC_LANG >= 201103L))
       #define HXCPP_OVERRIDE override
    #else
       #define HXCPP_OVERRIDE

include/hxcpp.h

@@ -98,7 +98,7 @@
   #endif
 #endif
 
-#if __cplusplus >= 201103L || (defined(_MSC_VER) && _MSVC_LANG >= 201103L)
+#if HXCPP_API_LEVEL >= 500 && (__cplusplus >= 201103L || (defined(_MSC_VER) && _MSVC_LANG >= 201103L))
   #define HXCPP_OVERRIDE override
 #else
   #define HXCPP_OVERRIDE