In many places, we incorrectly used allBuildInfo, which
returns all BuildInfos that are buildable, and not
necessarily the ones we are actually going to *build*.
This used to "mostly do the right thing" because we
literally edited the PackageDescription to nub out things,
so you wouldn't see non-enabled components anyway.  However
when I added support for per-component configure, I stopped
editing the PackageDescription, which meant all of these
uses were wrong.

So, I updated them to do the right thing. Note that there
are still uses of allBuildInfo in Check, but that probably
requires a closer look.

Fixes #3847.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>