* internal.h: do not use ruby_sized_xrealloc() and ruby_sized_xfree()
  if HAVE_MALLOC_USABLE_SIZE (or _WIN32) is defined.
  We don't need these function if malloc_usable_size() is available.
* gc.c: catch up this change.
* gc.c: define HAVE_MALLOC_USABLE_SIZE on _WIN32.
* array.c (ary_resize_capa): do not use ruby_sized_xfree() with
  local variable to avoid "unused local variable" warning.
  This change only has few impact.
* string.c (rb_str_resize): ditto.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43839 b2dd03c8-39d4-4d8f-98ff-823fe69b080e