Add in a definition for RTYPEDDATA_P for Ruby<1.9.3

This definition ensures the SWIG wrappers keep compiling in older versions
of Ruby given the previous change (which uses RTYPEDDATA_P and hence
requires Ruby 1.9.3). The definition of RTYPEDDATA_P is such that the
previous commit plus the definition should keep the behaviour the same
as before.

CHANGES.current

@@ -7,6 +7,9 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.0.0 (in progress)
 ===========================
 
+2019-02-22: tamuratak
+            #984 Add support for RTypedData introduced in Ruby 1.9.3.
+
 2019-02-21: wsfulton
             #1240 Suppress Java 9 deprecation warnings on finalize method.
 

Lib/ruby/rubyhead.swg

@@ -91,6 +91,9 @@
 #ifndef RSTRUCT_PTR
 # define RSTRUCT_PTR(x) RSTRUCT(x)->ptr
 #endif
+#ifndef RTYPEDDATA_P
+# define RTYPEDDATA_P(x) (TYPE(x) != T_DATA)
+#endif