Path issue with libuv 1.21

[lthms]

The current version of libuv for Archlinux is 1.21.

It looks like the include hierarchy has changed, and the package does not compile anymore. For instance, this line is wrong, because the uv-errno.h is now uv/errno.h as far as I can tell.

Note: I was able to build cl-libuv (and therefore cl-async) by just modifying uv-errno.h by uv/errno.h.