This patch is meant for core-updates since it rebuilds every LLVm
dependent, so more than 1000+ packages.  I've only tested against master
though.

It's not ready yet.

Since LLVM@10 takes a long time to compile, it's cumbersome to iterate
against it.
Instead, I found out that LLVM@3.5 builds much faster and the `pure'
package is a great candidate for testing.

I've added ("llvm" llvm-3.5 "lib") to the dependencies of pure.
But ("llvm" llvm-3.5) must be included as a native input because that's
where the C headers (include) files are.

The end result still depends on llvm "out" because the .so files has
references to the headers.

We could move the headers to a separate output, but LLVM@10 headers are
17MiB big already, so I'd rather not include them in the closure of
every package.

Any idea how to remove them?

-- 
Pierre Neidhardt
https://ambrevar.xyz/