[libc] Bring libc in-tree

Moving libc from its separate repo into this one, minor resulting build
fixes, and a hacky way to add -I for libc headers in builds.

src/kernel/console.h

@@ -1,5 +1,4 @@
 #pragma once
-#include <algorithm>
 #include <stdarg.h>
 #include <stdint.h>
 
@@ -61,7 +60,7 @@ void console::put_hex(T x, int width, char pad)
 	int len = 1;
 	for (int i = chars - 1; i >= 0; --i) {
 		uint8_t nibble = (x >> (i*4)) & 0xf;
-		if (nibble) len = std::max(i + 1, len);
+		if (nibble) len = len > i + 1 ? len : i + 1;
 		message[chars - i - 1] = digits[nibble];
 	}
 	message[chars] = 0;

src/kernel/memory_bootstrap.cpp

@@ -1,4 +1,3 @@
-#include <algorithm>
 #include <utility>
 
 #include "kernel_args.h"

src/kernel/page_manager.cpp

@@ -1,5 +1,3 @@
-#include <algorithm>
-
 #include "kutil/assert.h"
 #include "kutil/vm_space.h"
 #include "console.h"

src/kernel/scheduler.cpp

@@ -1,3 +1,5 @@
+#include <stddef.h>
+
 #include "apic.h"
 #include "clock.h"
 #include "console.h"