Deserialization recovery lead the compiler to drop public constructors
overridding internal constructors. This limits the logic to dropping the
overriding relationship instead of the whole constructor. This applies
when the overriden constructor fails to deserialize and only when the
overriding relationship was marked as not affecting ABI.
rdar://104704832
This change reflects the behavior of `DeclAttribute.printImpl` that
prints the `override` keyword in a swiftinterface only when the
overriden decl is also public.
This issue was detected when working on deserialization safety by public
overrides of private functions in the following tests:
test/Interpreter/vtables_multifile.swift
test/Interpreter/vtables_multifile_testable.swift
test/SILGen/accessibility_vtables_testable.swift
test/SILGen/accessibility_vtables_usableFromInline.swift
test/SILGen/vtables_multifile.swift
