Non-POSIX `CLOCK` enum members have been removed from `core.sys.posix.time`

Namely `CLOCK_MONOTONIC_RAW`, `CLOCK_MONOTONIC_COARSE` (linux),
`CLOCK_MONOTONIC_PRECISE`, `CLOCK_MONOTONIC_FAST` (FreeBSD, DragonflyBSD),
and `CLOCK_MONOTONIC_COARSE` (CRuntime_Glibc).
Those were deprecated in 2.067.
They are available on their respective platform modules.
