* struct.c (struct_make_members_list): extract making member name
	  list from char* va_list, with creating symbols without
	  intermediate IDs.

	* struct.c (struct_make_members_list, rb_struct_s_def): member
	  names should be unique. [ruby-core:74971] [Bug #12291]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@54637 b2dd03c8-39d4-4d8f-98ff-823fe69b080e