When running "go test" including a main package which has a PGO
profile, we currently build the package being tested and its
dependencies with PGO, but we failed to attach the profile to
test-only dependencies. If a package is (transitively) imported
by both the package being tested and the test, the PGO version
and the non-PGO version of the package are both linked into the
binary, causing link-time error.
This CL fixes this by attaching the PGO profile to dependencies of
the test.