mruby-io: provide Kernel#p in this gem

To prevent ordering instability when output from mruby-io and Kernel#p
mixed.

mrbgems/mruby-io/mrblib/kernel.rb

@@ -13,6 +13,17 @@ module Kernel
     end
   end
 
+  private def p(*a)
+    for e in a
+      $stdout.write e.inspect
+      $stdout.write "\n"
+    end
+    len = a.size
+    return nil if len == 0
+    return a[0] if len == 1
+    a
+  end
+
   private def print(...)
     $stdout.print(...)
   end

src/kernel.c

@@ -551,6 +551,7 @@ mrb_obj_ceqq(mrb_state *mrb, mrb_value self)
 // ISO 15.3.1.3.35 Kernel#print
 mrb_value mrb_print_m(mrb_state *mrb, mrb_value self);
 
+#ifndef HAVE_MRUBY_IO_GEM
 // ISO 15.3.1.2.9   Kernel.p
 // ISO 15.3.1.3.34  Kernel#p
 //
@@ -570,6 +571,7 @@ mrb_p_m(mrb_state *mrb, mrb_value self)
   if (argc == 1) return argv[0];
   return mrb_ary_new_from_values(mrb, argc, argv);
 }
+#endif
 
 void
 mrb_init_kernel(mrb_state *mrb)
@@ -603,8 +605,8 @@ mrb_init_kernel(mrb_state *mrb)
   mrb_define_method_id(mrb, krn, MRB_SYM_Q(kind_of),                  mrb_obj_is_kind_of_m,            MRB_ARGS_REQ(1));    /* 15.3.1.3.26 */
   mrb_define_method_id(mrb, krn, MRB_SYM_Q(nil),                      mrb_false,                       MRB_ARGS_NONE());    /* 15.3.1.3.32 */
   mrb_define_method_id(mrb, krn, MRB_SYM(object_id),                  mrb_obj_id_m,                    MRB_ARGS_NONE());    /* 15.3.1.3.33 */
-  mrb_define_private_method_id(mrb, krn, MRB_SYM(p),                  mrb_p_m,                         MRB_ARGS_ANY());     /* 15.3.1.3.34 */
 #ifndef HAVE_MRUBY_IO_GEM
+  mrb_define_private_method_id(mrb, krn, MRB_SYM(p),                  mrb_p_m,                         MRB_ARGS_ANY());     /* 15.3.1.3.34 */
   mrb_define_private_method_id(mrb, krn, MRB_SYM(print),              mrb_print_m,                     MRB_ARGS_ANY());     /* 15.3.1.3.35 */
 #endif
   mrb_define_private_method_id(mrb, krn, MRB_SYM(raise),              mrb_f_raise,                     MRB_ARGS_OPT(2));    /* 15.3.1.3.40 */