ordering when building multiple dependent packages

[djugei]

rua 0.19.10

i wanted to run a rua upgrade.
both signal-cli and libsignal-client needed upgrades.
signal-cli depends on libsignal-client.

rua tried to build both and then install both.
the build of signal-cli failed with confusing error messages.
this then aborted the entire upgrade.
after a while i figured out that the api provided by libsignal-client changed.
i manually updated libsignal-client first, and then updated rua.

rua should have split the upgrade into multiple steps, where in each step n-1 must have built and installed all (build-)dependencies of step n

i am somewhat willing to write a pr if that is welcome, though i have no experience with the codebase.

[arodland]

Likewise, rakudo depends on nqp>=$pkgver and nqp depends on moarvm>=$pkgver. When all three get a new version, rua tries to build all three before installing anything, meaning that two out of the three builds fail. In pkgbuild all depends are implicitly build-depends, so in this scenario we need to build moarvm, install, build nqp, install, build rakudo, install.