Make core/ includes absolute, remove subfolders from include path

This allows more consistency in the manner we include core headers,
where previously there would be a mix of absolute, relative and
include path-dependent includes.

drivers/unix/dir_access_unix.cpp

@@ -32,18 +32,19 @@
 
 #if defined(UNIX_ENABLED) || defined(LIBC_FILEIO_ENABLED)
 
-#ifndef ANDROID_ENABLED
-#include <sys/statvfs.h>
-#endif
-
 #include "core/list.h"
-#include "os/memory.h"
-#include "print_string.h"
+#include "core/os/memory.h"
+#include "core/print_string.h"
+
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
+#ifndef ANDROID_ENABLED
+#include <sys/statvfs.h>
+#endif
+
 #ifdef HAVE_MNTENT
 #include <mntent.h>
 #endif