Mirror changes from dotnet/corert,corefx

[Dotnet-GitSync-Bot]

This PR contains mirrored changes from dotnet/corert,corefx

Please REBASE this PR when merging

cc @filipnavara

[filipnavara]

@karelz What's the process for labeling something with netfx-port-consider? This is broken on NetFX as shown by unit tests in dotnet/corefx#34818.

[karelz]

@filipnavara we do not use that label anymore. I was planning to delete it eventually.
We will consider porting bug fixes which have high business impact on customers (either large number of customers, or significant segment of customers) without reasonable workaround to .NET Framework. That can be done ad-hoc.
If you are adding test and it fails on .NET Framework, first make sure it is truly bug in .NET Framework (and not in .NET Core or in the test), then disable the test on .NET Framework.

[filipnavara]

If you are adding test and it fails on .NET Framework, first make sure it is truly bug in .NET Framework (and not in .NET Core or in the test),

I checked with reference source it is exactly the same bug that was fixed in CoreCLR.

then disable the test on .NET Framework.

Done.

The impact for customers is likely minimal and there are workarounds so it's not likely to meet the bar for backport, but I wanted to check nevertheless.

[karelz]

Thanks @filipnavara! I love it when people ask for not-quite-certain-things first ... IMO a very good practice ;)