libuv users are only supposed to directly include uv.h. In v1.21.0, all
the uv-*.h headers were renamed to uv/*.h, which caused the unit tests
to fail with
[123/125] Generating post/uv-errno.h
FAILED: test/includes/post/uv-errno.h
cd «SRCDIR»/src/neovim/build/test/includes && /usr/bin/clang -std=c99 -E -P «SRCDIR»/src/neovim/test/includes/pre/uv-errno.h -I/usr/include -I/usr/include -o «SRCDIR»/neovim/build/test/includes/post/uv-errno.h
«SRCDIR»/src/neovim/test/includes/pre/uv-errno.h:1:10: error: 'uv-errno.h' file not found with <angled> include; use "quotes" instead
#include <uv-errno.h>
^~~~~~~~~~~~
"uv-errno.h"
The intention of the file is to extend libuv's error constants with more
values used by the unit tests. This can just as easily be achieved
without poking into pseudo-private header files.
Replaced old unit tests for errno with libuv error codes UV_ENOENT
and UV_EEXIST (for os_open and os_getperms).
Added libuv include path to test/includes compiler calls - needed
to get hold of libuv headers.
