[libc] Add new libc

This new libc is mostly from scratch, with *printf() functions provided
by Marco Paland and Eyal Rozenberg's tiny printf library, and malloc and
friends provided by dlmalloc.

src/kernel/assert.cpp

@@ -16,6 +16,6 @@ install(uintptr_t entrypoint, const void *symbol_data)
 } // namespace panic
 
 extern "C"
-void _PDCLIB_assert(const char *message, const char *function, const char *file, unsigned line) {
+void __assert_fail(const char *message, const char *file, unsigned line, const char *function) {
     panic::panic(message, nullptr, function, file, line);
 }

src/kernel/frame_allocator.h

@@ -2,6 +2,7 @@
 /// \file frame_allocator.h
 /// Allocator for physical memory frames
 
+#include <stddef.h>
 #include <stdint.h>
 #include <util/spinlock.h>