Add a new (internal) feature test macro to detect whether the wrappers are no-ops on a given platform.

Note that one-arg __builtin_prefetch(x) is equivalent to __builtin_prefetch(x, 0, 3), per `man BUILTIN_PREFETCH(3)` and gcc docs.

PiperOrigin-RevId: 449508660
Change-Id: I144e750205eec0c956d8dd62bc72e10bdb87c4f7