Use a more direct way for NATIVE_RSTRING_PTR

(cherry picked from commit 39f5275)

Author: eregon

lib/cext/include/truffleruby/truffleruby.h

@@ -158,7 +158,7 @@ int rb_encdb_alias(const char *alias, const char *orig);
 VALUE rb_ivar_lookup(VALUE object, const char *name, VALUE default_value);
 
 // Additional macro to make sure the RSTRING_PTR and the bytes are in native memory, for testing.
-#define NATIVE_RSTRING_PTR(str) ((char*) polyglot_as_i64(polyglot_invoke(RSTRING_PTR(str), "polyglot_address")))
+#define NATIVE_RSTRING_PTR(str) ((char*) polyglot_as_i64(RUBY_CEXT_INVOKE_NO_WRAP("NATIVE_RSTRING_PTR", str)))
 
 // Inline implementations
 

lib/truffle/truffle/cext.rb

@@ -1854,6 +1854,10 @@ def RSTRING_PTR(string)
     RStringPtr.new(string)
   end
 
+  def NATIVE_RSTRING_PTR(string)
+    TrufflePrimitive.string_pointer_to_native(string)
+  end
+
   def RSTRING_END(string)
     RStringEndPtr.new(string)
   end