marshal.c: use STATIC_ASSERT

* marshal.c (MARSHAL_INFECTION): check size by STATIC_ASSERT.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51938 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

marshal.c

@@ -148,7 +148,7 @@ rb_marshal_define_compat(VALUE newclass, VALUE oldclass, VALUE (*dumper)(VALUE),
 }
 
 #define MARSHAL_INFECTION FL_TAINT
-typedef char ruby_check_marshal_viral_flags[MARSHAL_INFECTION == (int)MARSHAL_INFECTION ? 1 : -1];
+STATIC_ASSERT(marshal_infection_is_int, MARSHAL_INFECTION == (int)MARSHAL_INFECTION);
 
 struct dump_arg {
     VALUE str, dest;