GC SOS commands are failing on macOS.

[mikem8361]

In the SOS.UnitTests, various commands are failing on macOS. These failures need to be fixed and that the SOSRunner doesn't detect these kind of failures.

(lldb) runcommand sos DumpObj -refs 000000018201fa58
Name:        GCWhere
MethodTable: 00000001084251a8
EEClass:     0000000109031098
Size:        24(0x18) bytes
File:        /Users/mikem/diagnostics/artifacts/Debuggees/GCWhere/bin/Debug/netcoreapp2.0/publish/GCWhere.dll
Fields:
              MT    Field   Offset                 Type VT     Attr            Value Name
0000000108dc5ba0  4000001        8        System.String  0 instance 000000018201fa18 _string
GC Refs:
              offset object
Failed to request number of entries.
DumpObj -refs 000000018201fa58  failed

None

(lldb) runcommand sos GCRoot -all 000000018201fa58
Failed to request number of entries.Thread 5948bc:
    00007FFF5FBF6F00 00000001090404E2 GCWhere.Main() [/Users/mikem/diagnostics/artifacts/Debuggees/GCWhere/GCWhere.cs @ 33]
        rbp-18: 00007fff5fbf6f08
            ->  000000018201FA58 <unknown>

    00007FFF5FBF6F00 00000001090404E2 GCWhere.Main() [/Users/mikem/diagnostics/artifacts/Debuggees/GCWhere/GCWhere.cs @ 33]
        rbp-8: 00007fff5fbf6f18
            ->  000000018201FA58 <unknown>

Failed to request number of entries.Failed to request number of entries.Failed to request number of entries.Failed to request number of entries.Found 2 roots.

None

[mikem8361]

These tests failed on 2.1.0 and 2.0.9 but not on 1.0.9.