swift

a892e899 - [GSB] Simplify and clean up RequirementSource::isSelfDerivedSource().

[GSB] Simplify and clean up RequirementSource::isSelfDerivedSource(). Reimplement isSelfDerivedSource() in terms of the new visitPotentialArchetypesAlongPath(). Aside from being clearer and shorter, this formulation eliminates some hackery (the direct "NestedType" lookup) that was mostly masking a bug in updateNestedTypeForConformance() where we created a nested-type-name-match source with an incorrect source for the purposes of concretizing the nested type. Fixes SR-4458 / rdar://problem/31375569.