pidfd_open.2, pidfd_send_signal.2, poll.2, semget.2: ffix: EXAMPLES: use .EX/.EE instead of .nf/.fi

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/pidfd_open.2

@@ -208,7 +208,7 @@ event.
 .\"
 .SS Program source
 \&
-.nf
+.EX
 #define _GNU_SOURCE
 #include <sys/types.h>
 #include <sys/syscall.h>
@@ -259,7 +259,7 @@ main(int argc, char *argv[])
     close(pidfd);
     exit(EXIT_SUCCESS);
 }
-.fi
+.EE
 .SH SEE ALSO
 .BR clone (2),
 .BR kill (2),

man2/pidfd_send_signal.2

@@ -177,7 +177,7 @@ if that process terminates,
 fails with the error
 .BR ESRCH .
 .SH EXAMPLES
-.nf
+.EX
 #define _GNU_SOURCE
 #include <limits.h>
 #include <signal.h>
@@ -244,7 +244,7 @@ main(int argc, char *argv[])
 
     exit(EXIT_SUCCESS);
 }
-.fi
+.EE
 .SH SEE ALSO
 .BR clone (2),
 .BR kill (2),

man2/poll.2

@@ -569,7 +569,7 @@ at which point the file descriptor was closed and the program terminated.
 .\"
 .SS Program source
 \&
-.nf
+.EX
 /* poll_input.c
 
    Licensed under GNU General Public License v2 or later.
@@ -655,7 +655,7 @@ main(int argc, char *argv[])
     printf("All file descriptors closed; bye\en");
     exit(EXIT_SUCCESS);
 }
-.fi
+.EE
 .SH SEE ALSO
 .BR restart_syscall (2),
 .BR select (2),

man2/semget.2

@@ -397,7 +397,7 @@ ID = 9
 .in
 .SS Program source
 \&
-.nf
+.EX
 /* t_semget.c
 
    Licensed under GNU General Public License v2 or later.
@@ -456,7 +456,7 @@ main(int argc, char *argv[])
 
     exit(EXIT_SUCCESS);
 }
-.fi
+.EE
 .SH SEE ALSO
 .BR semctl (2),
 .BR semop (2),