PR libstdc++/56267
* include/bits/hashtable.h (__cache_default): Do not depend on
whether the hash function is DefaultConstructible or CopyAssignable.
(_Hashtable): Adjust static assertions.
* doc/xml/manual/containers.xml (containers.unordered.cache): Update.
* testsuite/23_containers/unordered_set/instantiation_neg.cc: Adjust
dg-error line number.
* testsuite/23_containers/unordered_set/
not_default_constructible_hash_neg.cc: Remove.
From-SVN: r206904