Ports: Add libuv

We've had a half-arsed port of libuv inside the cmake port, but let's
just port it properly.
Note that this pins a specific commit (which is currently the latest
commit in their default branch).

Ports/libuv/patches/0001-unix-Stub-out-get-set-priority-for-serenity.patch

@@ -0,0 +1,39 @@
+From 5ac8ded61c9bcddb7b1df3ad8a23b90a777349bc Mon Sep 17 00:00:00 2001
+From: Ali Mohammad Pur <ali.mpfard@gmail.com>
+Date: Fri, 9 Jul 2021 04:44:26 +0430
+Subject: [PATCH 1/7] unix: Stub out {get,set}priority for serenity
+
+---
+ src/unix/core.c | 6 ++++++
+ 1 file changed, 6 insertions(+)
+
+diff --git a/src/unix/core.c b/src/unix/core.c
+index 71e9c52..004a589 100644
+--- a/src/unix/core.c
++++ b/src/unix/core.c
+@@ -1421,7 +1421,11 @@ int uv_os_getpriority(uv_pid_t pid, int* priority) {
+     return UV_EINVAL;
+ 
+   errno = 0;
++#ifndef __serenity__
+   r = getpriority(PRIO_PROCESS, (int) pid);
++#else
++  r = 1;
++#endif
+ 
+   if (r == -1 && errno != 0)
+     return UV__ERR(errno);
+@@ -1435,8 +1439,10 @@ int uv_os_setpriority(uv_pid_t pid, int priority) {
+   if (priority < UV_PRIORITY_HIGHEST || priority > UV_PRIORITY_LOW)
+     return UV_EINVAL;
+ 
++#ifndef __serenity__
+   if (setpriority(PRIO_PROCESS, (int) pid, priority) != 0)
+     return UV__ERR(errno);
++#endif
+ 
+   return 0;
+ }
+-- 
+2.32.0
+