We need to propagate msbuild verbose level (-verbosity:level option) into illink.

The proposed mapping between msbuild verbosity and MessageCategory

q[uiet] >= MessageCategory.Error (not sure about this one)
d[etailed] >= MessageCategory.Info
diag[nostic] >= MessageCategory.Diagnostic

This should be done for illink task only, the command line interface for illink should still use -v to print everything

@vitek-karas how do you plan to use warning? If we go with an explicit -nowarn option we would need to expose that on VS UI.