[reg] Fix 13210 : libphobos2.so not being built

Accidental side effect from changes in https://github.com/D-Programming-Language/phobos/pull/2345 : target for `libphobos2.so` symlink never got referenced and thus never got executed.

This PR defines a bit more strict dependency sequence `dll -> libphobos2.so -> libbphobos2.so.0.66.0`

@MartinNowak please confirm is does not interfere with actual fix

@AndrewEdwards FYI
I cannot agree with you there. I've been busy building, RC1 for the last 4+ hours. Martin's response to a three day old request for input just arrived 22 minutes ago. That's four hours too late and consequently renders my last four hours useless since I have to now merge #2387 and start over. No complaints from me though, I really appreciate the continued support. I definitely could no do what I need to without you guys.