libstdc++: Add more Doxygen comments and another test for std::out_ptr
Improve Doxygen comments for std::out_ptr etc. and add a test for the
feature test macro. Also remove a redundant preprocessor condition.
Ideally the docs for std::out_ptr and std::inout_ptr would show examples
of how to use them and what they do, but that would take some effort.
I'll aim to do that before GCC 14 is released.
libstdc++-v3/ChangeLog:
* include/bits/out_ptr.h: Add Doxygen comments. Remove a
redundant preprocessor condition.
* testsuite/20_util/smartptr.adapt/version.cc: New test.