Libstdc++ is already tested by Google's oss-fuzz project:
https://github.com/google/oss-fuzz/tree/master/projects/libstdcpp

But the coverage is limited to a single test for std::format:
https://github.com/pauldreik/stdfuzz/blob/main/format/one-arg.cpp

We should extend this to other parts of the library. Ideas:

filesystem::path construction and manipulation. Construct random paths from combinations of a, ., and /. Maybe also test with some operations that don't depend on the actual filesystem, e.g. weakly_canonical.

_Utf_view for every combination of char8_t, char16_t, char32_t, wchar_t as inputs and outputs. Construct random strings and ensure they can be parsed, and that ranges::equal(utf_view, utf_view | views::reverse | ranges::to<std::basic_string> views::reverse) i.e. we get the same sequence of elements when reversing the view.

It would be good to fuzz std::regex but the current implementation is too easy to crash with large inputs, which fuzzers are likely to trigger (RHEL-118681).