stringio.c: RB_INTEGER_TYPE_P

* ext/stringio/stringio.c (RB_INTEGER_TYPE_P): fallback definition
  for 2.3 or earlier.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58057 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/stringio/stringio.c

@@ -20,6 +20,10 @@
 #include <sys/fcntl.h>
 #endif
 
+#ifndef RB_INTEGER_TYPE_P
+# define RB_INTEGER_TYPE_P(c) (FIXNUM_P(c) || RB_TYPE_P(c, T_BIGNUM))
+#endif
+
 struct StringIO {
     VALUE string;
     rb_encoding *enc;