GC ETW fixes. The code for getting data for ETW and perf counter was written by different

GC ETW fixes. The code for getting data for ETW and perf counter was written by different
folks and was very intertwined. For full CLR we always have both defined but for coreclr
perf counters are not enabled so some things for ETW were just 0. Need to make sure when one
is not defined the rest are still getting the data they need.

Commit migrated from https://github.com/dotnet/coreclr/commit/fa2ff58d3198122cbbc216e0fd664d9e09120669