Debian 12 ships with a version of libstdc++ that declares a templated constructor of `std::function` with an rvalue-reference parameter. This is not yet supported by Swift.
rdar://125816354
While initializing a `std::function` that takes `const std::string&` as a parameter currently crashes, changing the parameter type to `std::string` should work fine.
Clang is using C++17 standard version by default since Clang 16.
Swift’s ClangImporter should do the same, to make sure that clients who run clang and then swiftc without explicit std version see consistent behavior.
rdar://125777068
This makes sure that `std::function` is imported consistently on supported platforms, and that it allows basic usage: calling a function with `callAsFunction`, initializing an empty function, and passing a function retrieved from C++ back to C++ as a parameter.
rdar://103979602
