This doesn't actually have any effect unless you also change the
predefined value of __cplusplus, as it's currently 201703L. But if
somebody does want to do that, the new headers will get processed now.
libstdc++-v3/ChangeLog:
* doc/doxygen/user.cfg.in (INPUT): Add <latch> and <semaphore>.
include/iostream \
include/istream \
include/iterator \
+ include/latch \
include/limits \
include/list \
include/locale \
include/ratio \
include/regex \
include/scoped_allocator \
+ include/semaphore \
include/set \
include/shared_mutex \
include/span \