rules/build-prog: Ensure programs depend upon their transitive deps

Previously programs only depended upon the direct dependencies; while I
would have thought that this would be sufficient, somehow we were
getting to the link step of building `ghc-pkg` before `ghc-boot-th` was
built (despite the fact that `ghc-boot` has a direct dependency on
`ghc-boot-th`).

See #12078.

(cherry picked from commit 5d80d141)