Transform readline into a globally accessible function.

libc/inc/readline.h

@@ -0,0 +1,14 @@
+/// @file readline.h
+/// @brief
+/// @copyright (c) 2014-2023 This file is distributed under the MIT License.
+/// See LICENSE.md for details.
+
+#include "stddef.h"
+
+/// @brief Reads a line from the file.
+/// @param fd the file descriptor.
+/// @param buffer the buffer where we place the line.
+/// @param buflen the length of the buffer.
+/// @param readlen the amount we read, if negative, we did not encounter a newline.
+/// @return 0 if we are done reading, 1 if we encountered a newline, -1 if otherwise.
+int readline(int fd, char *buffer, size_t buflen, ssize_t *read_len);