Add a cmake and libuv port

[Dennisbonke]

This PR adds the following ports:

• libuv, a direct dependency of cmake,
• cmake, the successor to the old-school configure scripts.

This PR is part of #33
This PR is blocked on #53
This PR is blocked on managarm/xbstrap#24
This PR is blocked on a new xbstrap release
This PR is blocked on managarm/mlibc#158
This PR is blocked on managarm/mlibc#159
This PR is blocked on managarm/mlibc#163
This PR is blocked on managarm/mlibc#164
This PR is blocked on a new mlibc release

[qookei]

Looks fine apart from the the comments.

Some more notes:

• uv__sendmmsg and uv__recvmmsg is only called if defined(__linux__) || defined(__FreeBSD__) || defined(__FreeBSD_kernel__).
• uv__preadv and uv__pwritev is called if !defined(HAVE_PREADV) && defined(__linux__) (HAVE_PREADV means it's one of {Dragon,Free,Open,Net}BSD).
• uv__dup3 is never called (only exists in linux-syscall.{c,h}), on a side note, dup3 is only called if it's Linux, NetBSD or FreeBSD and otherwise dup2 is used.
• uv__fs_copy_file_range is only called if defined(__linux__) and is emulated otherwise.
• as already commented, uv__statx is only used if defined(__linux__).
• uv__getrandom is only used when defined(__linux__).

Also, I am unsure about the copyright on the new managarm-* files.

[qookei]

LGTM, will merge after everything this is blocked on is done