struct.c: split make_struct

* struct.c (anonymous_struct, new_struct, setup_struct): split
  make_struct() for each purpose.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40269 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
struct.c: hide member names

* struct.c (rb_struct_define_without_accessor, rb_struct_define),
  (rb_struct_s_def): hide member names array.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40270 b2dd03c8-39d4-4d8f-98ff-823fe69b080e