Add dependency for gc build & clang-tidy on llvm build

[kurapov-peter]

Currently, those two start without waiting for llvm build job and thus fail.

[leshikus]

this is not possible using the default dependency mechanism because these are different workflows; I will think of something

[leshikus]

I can add a message on failure in the log to suggest restarting the pipeline

[lmontigny]

no good solution at the moment, github interface to restart the build.