CreateSymbolicLink within a task succeeds on 16.2.x without creating the link (does not happen on 15.9.x)

### Steps to reproduce

[MSBuildSymbolicLinkRepro.zip](https://github.com/microsoft/msbuild/files/3579332/MSBuildSymbolicLinkRepro.zip)

Extract the attached zip file and run:

```
msbuild Repro.proj
```

This uses kernel32.dll P/Invoke, which for some reason has a different behavior than it should.

### Expected behavior

CreateSymbolicLink should succeed (return non-zero value) iff it creates a link.

### Actual behavior

CreateSymbolicLink succeeds but no link is created.

### Environment data

Fails in `16.2.37902.0`.
Behaves as expected in `15.9.21.664`.