CoreCLR tests contain native DLLs which are passed to ILC

[nattress]

The CoreCLR tests are distributed as a zip of pre-compiled assemblies. We unzip this and pass the contents of each tests' folder to ILC as input assemblies. Some tests contain native binary DLLs, though, and ILC fails to load these, failing the test.

For now we have a work-around in the ILC front-end that skips native binaries. Long term we should not even pass these in to ILC.

This was not a problem until PR #2765 which requires us to specify inputs as inputs, not references. In multi-module mode, references are not compiled at all.