When you think about using the library from languages which don't link against libc by default (Go for example), then this is a significant difference.
Not only does it seem unlikely your program would have a terminal output and standard streams without having an OS, bestline still requires a libc. Just open `bestline.c` and you'll find:
#include <termios.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <unistd.h>
#include <setjmp.h>
#include <poll.h>
#include <assert.h>
#include <signal.h>
#include <fcntl.h>
#include <limits.h>Most of the defines can have a null implementation and the core will still work. They just need to be defined.
And the message I quoted says literally nothing about µc.