…ile" (#674)

* Updates for MSVC implementation of P1152R4 "deprecating volatile"

* Enable volatile deprecation warnings in STL's std and libcxx test suites

* `<any>`: `any_cast<T>` now returns `remove_cv_t<T>` because it's silly to have a cv-qualified return type (LWG issue submitted)
* `<optional>`: `optional<T>::value_or` now returns `remove_cv_t<T>` because it's silly to have a cv-qualified return type (LWG issue submitted).
* `<type_traits>`: suppress deprecation warnings around `_Implicitly_convert_to` so `_Implicitly_convert_to<volatile meow>(woof)` doesn't warn
* `<variant>`: Suppress deprecation warnings when forming the "imaginary" overload set `FUN` for the `variant(T&&)` constructor.
* Add the new warning C5215 "'%s' a function parameter with volatile qualified type is deprecated in C++20" to libc++'s "suppress deprecation warnings" macro and update llvm submodule reference.
* Skip libc++ test `containers/sequences/deque/deque.modifiers/insert_iter_iter.pass.cpp` after seeing one timeout too many in Contest logs.
* Suppress C5215 in `tr1/include/tfuns.h` which uses volatile function parameters, and in `tr1/functional4` altogether.
* Update skips for two libc++ tests that changed suffixes from `.sh.cpp` to `.pass.cpp`.

* Add a throwaway `addCompileFlags` function to `LibcxxTestFormat` to enable libc++ to continue working after upstream changes to pass configuration to the filesystem tests which we do not run.