cc -pipe -O   -pthread  -Wall -Wextra -Werror=implicit-function-declaration unistd/posix_close.c -o unistd/posix_close -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm -lpthread -lrt  -lrt -lcrypt
unistd/posix_close.c: In function 'main':
unistd/posix_close.c:9:7: error: implicit declaration of function 'posix_close'; did you mean 'pclose'? [-Werror=implicit-function-declaration]
  if ( posix_close(0, POSIX_CLOSE_RESTART) < 0 )
       ^~~~~~~~~~~
       pclose
unistd/posix_close.c:9:22: error: 'POSIX_CLOSE_RESTART' undeclared (first use in this function)
  if ( posix_close(0, POSIX_CLOSE_RESTART) < 0 )
                      ^~~~~~~~~~~~~~~~~~~
unistd/posix_close.c:9:22: note: each undeclared identifier is reported only once for each function it appears in
cc1: some warnings being treated as errors