Rollup merge of #114349 - inferiorhumanorgans:dragonfly-link-libz, r=cuviper

rustc_llvm: Link to `zlib` on dragonfly and solaris

On native builds `llvm-config` picks up `zlib` and this gets pased into
the rust build tools, but on cross builds `llvm-config` is explicitly
ignored as it contains information for the host system and cannot be
trusted to be accurate for the target system.

Both DragonFly and Solaris contain `zlib` in the base system, so this is
both a safe assumption and required for a successful cross build unless
`zlib` support is disabled in LLVM.

This is more or less in the same vein as rust-lang#75713 and rust-lang#75655.

Author: matthiaskrgr