Possible fix for max_align_t breakage in Travis CI

The Travis CI build is failing after an include of <cstddef> -- This is
an attempt to work around that by including <stddef.h> instead. Problem
not apparent in my FreeBSD environment.

runtime/Cpp/runtime/src/atn/LexerActionType.h

@@ -5,7 +5,7 @@
 
 #pragma once
 
-#include <cstddef>
+#include <stddef.h>
 
 namespace antlr4 {
 namespace atn {