Update PIDFD_* constants for Linux 6.9

Linux 6.9 adds some more PIDFD_* constants.  Add them to glibc's
sys/pidfd.h, including updating comments that said FLAGS was reserved
and must be 0, along with updating tst-pidfd-consts.py.

Tested with build-many-glibcs.py.

sysdeps/unix/sysv/linux/sys/pidfd.h

@@ -22,12 +22,14 @@
 #include <bits/types/siginfo_t.h>
 
 #define PIDFD_NONBLOCK O_NONBLOCK
+#define PIDFD_THREAD O_EXCL
+
+#define PIDFD_SIGNAL_THREAD (1UL << 0)
+#define PIDFD_SIGNAL_THREAD_GROUP (1UL << 1)
+#define PIDFD_SIGNAL_PROCESS_GROUP (1UL << 2)
 
 /* Returns a file descriptor that refers to the process PID.  The
-   close-on-exec is set on the file descriptor.
-
-   The FLAGS argument is reserved for future use, it must be specified
-   as 0.  */
+   close-on-exec is set on the file descriptor.  */
 extern int pidfd_open (__pid_t __pid, unsigned int __flags) __THROW;
 
 /* Duplicates an existing file descriptor TARGETFD in the process referred
@@ -39,10 +41,7 @@ extern int pidfd_getfd (int __pidfd, int __targetfd,
 			unsigned int __flags) __THROW;
 
 /* Sends the signal SIG to the target process referred by the PIDFD.  If
-   INFO points to a siginfo_t buffer, it will be populated.
-
-   The FLAGS argument is reserved for future use, it must be specified
-   as 0.  */
+   INFO points to a siginfo_t buffer, it will be populated.  */
 extern int pidfd_send_signal (int __pidfd, int __sig, siginfo_t *__info,
 			      unsigned int __flags) __THROW;
 

sysdeps/unix/sysv/linux/tst-pidfd-consts.py

@@ -39,7 +39,7 @@ def main():
         sys.exit (77)
 
     linux_version_headers = glibcsyscalls.linux_kernel_version(args.cc)
-    linux_version_glibc = (6, 8)
+    linux_version_glibc = (6, 9)
     sys.exit(glibcextract.compare_macro_consts(
                 '#include <sys/pidfd.h>\n',
                 '#include <asm/fcntl.h>\n'