Swift: Fix regression in linking to interface libraries

Since commit 2026915f8f (Swift: Propagate Swift_MODULE_DIRECTORY as include
directory, 2020-02-03, v3.18.0-rc1~547^2) we internally call
`GetAllConfigCompileLanguages` on all directly linked targets without
checking if they are interface libraries that don't compile at all.
That violates an internal assumption and assertion.

Fixes: #20977
2 files changed