The native compiler handled corrupted default parameter values by
substituting in default(T).  It's unclear if this was intentional
behavior in the compiler or not.

Either way though obfuscators took advantage of this behavior and at
least one prominent one will corrupt default parameter values when the
value is null.  Enough prominent libraries have shipped using such
obfuscators that it is a blocker to upgrading.  Hence we need to emulate
the native compiler behavior here.

This change is a bit large because I needed to update the test resources
with a corrupted DLL in order to test out the changes.

closes #4196