Filter instead of dropwhile to find recompile targets

[filmor]

This more of an RFC PR, I don't really understand why the dropwhile is used. In our case, we have a (dependency-free) library that is usually in _checkouts while developing that shows up roughly in the middle of the dependency list and results in a rebuild of most dependencies for every compile.

[ferd]

We recompile all the libs that depend on another one because recompiling it risks impacting features like parse transforms or .hrl files that would bubble up to higher level libraries that depend on them. Just filtering risks breaking builds when, for example, you upgrade lager but all the apps on top are stuck with the old compilation of their parse transform and record definitions.

[ferd]

I do agree however that the needs_compile could possibly be made smarter to know when you would need to bubble the compilation up the tree, but aside from _checkouts this never happens since we don't re-compile dependencies aside from the initial fetch and upgrades.

[filmor]

Well, as said, with the existing sorting, a _checkouts dependency can end up in the middle of the dependency list, and then we indeed do recompile possibly a lot of dependencies. I'll try to fix the sorting.