cc -pthread  -Wall -Wextra -Werror=implicit-function-declaration unistd/swab.c -o unistd/swab -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE -lm -lpthread -lrt -lintl -liconv
unistd/swab.c: In function ‘main’:
unistd/swab.c:13:9: error: implicit declaration of function ‘swab’ [-Wimplicit-function-declaration]
   13 |         swab(in, out, 4);
      |         ^~~~