pidfd: properly detect if libc offers pidfd syscalls and make use of them then

We never updated the meson checks when glibc finally learned about these
syscalls, address that.

meson.build

@@ -624,11 +624,13 @@ foreach ident : [
         ['pidfd_send_signal', '''#include <stdlib.h>
                                  #include <unistd.h>
                                  #include <signal.h>
-                                 #include <sys/wait.h>'''],
+                                 #include <sys/wait.h>
+                                 #include <sys/pidfd.h>'''],
         ['pidfd_open',        '''#include <stdlib.h>
                                  #include <unistd.h>
                                  #include <signal.h>
-                                 #include <sys/wait.h>'''],
+                                 #include <sys/wait.h>
+                                 #include <sys/pidfd.h>'''],
         ['rt_sigqueueinfo',   '''#include <stdlib.h>
                                  #include <unistd.h>
                                  #include <signal.h>

src/basic/pidref.c

@@ -1,5 +1,9 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
+#if HAVE_PIDFD_OPEN
+#include <sys/pidfd.h>
+#endif
+
 #include "errno-util.h"
 #include "fd-util.h"
 #include "missing_syscall.h"

src/libsystemd/sd-event/sd-event.c

@@ -1,6 +1,9 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
 #include <sys/epoll.h>
+#if HAVE_PIDFD_OPEN
+#include <sys/pidfd.h>
+#endif
 #include <sys/timerfd.h>
 #include <sys/wait.h>
 

src/libsystemd/sd-event/test-event.c

@@ -1,5 +1,8 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
+#if HAVE_PIDFD_OPEN
+#include <sys/pidfd.h>
+#endif
 #include <sys/wait.h>
 #include <unistd.h>
 

src/libsystemd/sd-login/test-login.c

@@ -1,6 +1,9 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
 #include <poll.h>
+#if HAVE_PIDFD_OPEN
+#include <sys/pidfd.h>
+#endif
 
 #include "sd-login.h"
 

src/login/pam_systemd.c

@@ -10,6 +10,9 @@
 #include <security/pam_modules.h>
 #include <security/pam_modutil.h>
 #include <sys/file.h>
+#if HAVE_PIDFD_OPEN
+#include <sys/pidfd.h>
+#endif
 #include <sys/stat.h>
 #include <sys/sysmacros.h>
 #include <sys/types.h>

src/test/test-aux-scope.c

@@ -3,6 +3,9 @@
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
+#if HAVE_PIDFD_OPEN
+#include <sys/pidfd.h>
+#endif
 #include <sys/wait.h>
 
 #include "sd-event.h"