libstdc++: Fix <memory> for -std=c++23 -ffreestanding [PR114866]

std::shared_ptr isn't declared for freestanding, so guard uses of it
with #if _GLIBCXX_HOSTED in <bits/out_ptr.h>.

libstdc++-v3/ChangeLog:

	PR libstdc++/114866
	* include/bits/out_ptr.h [!_GLIBCXX_HOSTED]: Don't refer to
	shared_ptr, __shared_ptr or __is_shred_ptr.
	* testsuite/20_util/headers/memory/114866.cc: New test.