[libc++] Qualify calls to nullary functions like __throw_foo (#122465)

This is technically not necessary in most cases to prevent issues with ADL,
but let's be consistent. This allows us to remove the libcpp-qualify-declval
clang-tidy check, which is now enforced by the robust-against-adl clang-tidy check.

GitOrigin-RevId: 5e26fb169936ca1e24da6698ce895fec99af06c2