This replaces the use of `isExpansionInMainFile` with instead taking the list of input files, and only touching them. This doesn't keep `isExpansionInMainFile` because it should be redundant, and as such it'd be easy to forget. Unless it starts being a performance issue, it's probably better to omit.
This picks up a newer version of LLVM and the LLVM Bazel integration.
The big change here is that we can configure the LLVM targets that are
built, which allows us to dramatically reduce the build costs by
focusing on a couple of CPUs for the time being.
There are a few API updates needed as well.
This also rotates the cache version so we start with a clean Bazel cache
from here. Otherwise we'd potentially pay the cost of carrying around
stale bits of LLVM endlessly.
Jon Meow
Chandler Carruth