implemented file read/write functions

src/filesystem/internal.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include "tlibc/filesystem.h"
+#if TLIBC_FS_USE_WINDOWS_H
+#include <windows.h>
+#else
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#endif