libstdc++: Fix a few !HOSTED test regressions
libstdc++-v3/ChangeLog:
* testsuite/20_util/to_chars/version.cc: Mark hosted-only.
* testsuite/20_util/uses_allocator/lwg3677.cc: Ditto.
* testsuite/20_util/weak_ptr/cons/self_move.cc: Ditto.
* testsuite/std/ranges/adaptors/as_rvalue/1.cc: Replace usage of
std::make_unique with a freestanding-compatible wrapper around
unique_ptr.
* testsuite/21_strings/basic_string_view/operations/contains/char.cc:
Don't test for presence of __cpp_lib_string_contains on !HOSTED.
* testsuite/21_strings/basic_string_view/operations/contains/char/2.cc:
Ditto.
* testsuite/std/ranges/version_c++23.cc: Don't test for presence
of __cpp_lib_ranges in !HOSTED.