Allow transitive include of <optional> in affected headers

Author: winner245

libcxx/include/experimental/iterator

@@ -127,6 +127,7 @@ _LIBCPP_POP_MACROS
 #  if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
 #    include <cstddef>
 #    include <iosfwd>
+#    include <optional>
 #    include <type_traits>
 #  endif
 #endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)

libcxx/include/mutex

@@ -504,6 +504,7 @@ _LIBCPP_POP_MACROS
 #    include <initializer_list>
 #    include <iosfwd>
 #    include <new>
+#    include <optional>
 #    include <stdexcept>
 #    include <system_error>
 #    include <type_traits>

libcxx/include/shared_mutex

@@ -457,6 +457,7 @@ _LIBCPP_POP_MACROS
 #  endif // _LIBCPP_HAS_THREADS
 
 #  if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
+#    include <optional>
 #    include <system_error>
 #  endif
 #endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)