(https://github.com/dotnet/corert/pull/2485), which ports a number of GC changes done within the last month or two from CoreCLR to CoreRT. The only changes to anything in Native/gc are:
1. Move an assert under #ifndef FEATURE_REDHAWK since it only is a useful assert on CoreCLR (https://github.com/dotnet/corert/pull/2485#issuecomment-271975502)
2. Add UNREFERENCED_PARAMETERs to things in gc.cpp and elsewhere that were producing warnings
All other changes in Native/gc are directly from CoreCLR without modification. I have validated that I am able to do PerfView GC analysis with these changes (since the CoreCLR changes touched ETW eventing).
[tfs-changeset: 1644465]
