Kernel+LibC: Add some errno codes

Kernel now returns ENOMEM and other errnos, so we dont have to write
error messages

libc/include/errno.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <sys/cdefs.h>
+
+#define ENOMEM 1
+#define EINVAL 2
+#define ENOTDIR 3
+#define EISDIR 4
+#define ENOENT 5
+#define EIO 6
+
+__BEGIN_DECLS
+
+extern int errno;
+
+__END_DECLS

libc/include/string.h

@@ -19,4 +19,6 @@ char* strncpy(char* __restrict, const char* __restrict, size_t);
 
 char* strstr(const char*, const char*);
 
+char* strerror(int);
+
 __END_DECLS