Use a 64-bit overflow test. Wait only for sampling core PMCs. Accept a sampling PMC that an NMI stopped.

Sponsored by: AMD

GENERIC with INVARIANTS on AMD, 160 CPUs.
51 PMC tests pass, with no failures or skips.
Full stack: 59 tests, 200 start/stop cycles, and 40 active unloads pass.
All prefixes build. Old/new log checks pass.