Trying again to fix the broken 1.9.3 compile.

Author: jdantonio

ext/concurrent_ruby_ext/common.h

@@ -3,6 +3,8 @@
 // https://github.com/ruby/ruby/blob/ruby_2_0_0/include/ruby/intern.h
 // rb_check_arity was added in Ruby 2.0
 
+#define UNLIMITED_ARGUMENTS (-1)
+
 #define rb_check_arity(argc, min, max) do { \
   if (((argc) < (min)) || ((argc) > (max) && (max) != UNLIMITED_ARGUMENTS)) \
   rb_error_arity(argc, min, max); \