struct.c: use iseqval

* struct.c (define_aref_method, define_aset_method): use iseq
  VALUE instead of rb_iseq_t to prevent from GC, as RB_GC_GUARD
  makes sense only for local variables.  [Feature #10575]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48754 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test_cstr.rb: all wchar encodings

* test/-ext-/string/test_cstr.rb (assert_wchars_term_char): test
  for all wide char encodings.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48755 b2dd03c8-39d4-4d8f-98ff-823fe69b080e