clangd compilation server

[kyle]

https://reviews.llvm.org/rL294291

This is a concept that I think was discussed a couple of years ago.  It provides the compiler as a service rather than a library.   I thought it was an interesting idea back when it was first mentioned, but now someone has done it for Clang.

[bas]

Thanks for mentioning it here. I did catch something of it some time ago. This solution is nice for large C/C++ codebases
where compilation times are non-trivial. For C2 I haven't even found a good reason to multi-thread yet... (1.8 Mloc/sec parsing,
800Kloc/sec with analysis). Since the latest vim (7 if I remember correctly) they support pipes that can be used by plugins
to for example talk to a persistent server/daemon like this..