[MS] Don't reference deleted copy ctors from catchable types

When throwing objects with deleted copy constructors, the copy ctor
field of the catchable type should remain null and the mangle name
changes. This already worked in simple cases, but in cases involving
non-trivial subobjects, sometimes LookupCopyingConstructor could return
a non-null but deleted constructor decl. Skip those and don't reference
them.

Fixes PR43680