FS-6293: srcdir builds, don't touch src/include/switch.h in builddir, it creates an empty one that is included before the real one
silence clang warning about always false, this is meant to keep naughty users for the api from causing a crash, the check is fine
we are intentionally using a value outside of the enum here as a special value.  The compiler will always make this an int anyways, so this is safe.  cast to remove the warning