libstdc++: Fix -Wmismatched-tags warnings (PR 96063)

libstdc++: Fix -Wmismatched-tags warnings (PR 96063)

libstdc++-v3/ChangeLog:

	* include/bits/fs_dir.h: Use consistent tag in class-head.
	* include/bits/localefwd.h: Likwise.
	* include/bits/regex.h: Likwise.
	* include/bits/stl_map.h: Likwise.
	* include/bits/stl_multimap.h: Likwise.
	* include/bits/stl_multiset.h: Likwise.
	* include/bits/stl_set.h: Likwise.
	* include/std/complex: Likwise.
	* include/std/functional: Likwise.
	* include/std/future: Likwise.
	* include/std/system_error: Likwise.
	* include/std/thread: Likwise.
	* include/std/tuple: Likwise.
	* include/std/type_traits: Likwise.
	* include/std/valarray: Likwise.