attribute const -> pure.

include/bx/macros.h

@@ -66,7 +66,7 @@
 #	define BX_UNLIKELY(_x) __builtin_expect(!!(_x), 0)
 #	define BX_NO_INLINE   __attribute__( (noinline) )
 #	define BX_NO_RETURN   __attribute__( (noreturn) )
-#	define BX_CONST_FUNC  __attribute__( (const) )
+#	define BX_CONST_FUNC  __attribute__( (pure) )
 
 #	if BX_COMPILER_GCC >= 70000
 #		define BX_FALLTHROUGH __attribute__( (fallthrough) )