build: link Yams privately

Because Yams is used with `@_implementationOnly`, the clients of
`SwiftDriver` do not need to link against `Yams` or `CYaml`.  This was
uncovered when building SourceKit-LSP.

Author: compnerd

Sources/SwiftDriver/CMakeLists.txt

@@ -83,7 +83,8 @@ target_link_libraries(SwiftDriver PUBLIC
   TSCBasic
   TSCUtility
   SwiftOptions
-  llbuildSwift
+  llbuildSwift)
+target_link_libraries(SwiftDriver PRIVATE
   CYaml
   Yams)