Use RtlUnwind instead of RtlUnwindEx.

[jaykrell]

Because the formerly uninitialized scratch context is now an input.

[Dotnet-GitSync-Bot]

I couldn't figure out the best area label to add to this PR. Please help me learn by adding exactly one area label.

[jkotas]

Is this fixing any observable bug?

[janvorli]

This change doesn't seem necessary, RtlUnwindEx fills in the passed in context with the current context using RtlCaptureContext. RtlUnwind until very recent Windows 10 was implemented in the OS literally as we do in this function.

[jaykrell]

This code used to be correct, but is no longer.
In the current Windows 10 implementation, the context parameter to RtlUnwindEx is an input, and not merely uninitialized scratch.
So this is reading uninitialized data.
longjmp for example has received this same change.

[jkotas]

Ok, what does not work with the code that we have there today?

Note that this code is present in all .NET Framework and .NET Core runtimes shipped in last 15+ years.

[jaykrell]

It is not clearly deterministic.
It uses uninitialized stack.
Longjmp received the same change for the same reason.

[jaykrell]

It is also a little smaller but that isn’t the point.
It never needed to use RtlUnwindEx.
There was no advantage to that on older systems, given no already allocated context or history table.
It might as well use RtlUnwind.

[jkotas]

Ok, this looks like an improvement. Thanks