Issue Description:

If the directory name of the package under development collides with the final path component of a dependency, the package manager refuses to do anything, falsely reporting a cyclic dependency.

This three‐line script triggers it using the package manager’s own demonstration packages:

git clone https://github.com/apple/example-package-deckofplayingcards example-package-fisheryates
cd example-package-fisheryates
swift build

And this is the resulting complaint:

error: the package example-package-fisheryates[[...]/example-package-fisheryates] depends on itself
error: cyclic dependency declaration found: DeckOfPlayingCards -> DeckOfPlayingCards

The first half of the error does not always appear.

With --enable-pubgrub-resolver the only output is “Illegal instruction: 4” instead.