xattr-util: use crtime/btime if statx() is available for implementation of fd_setcrtime() and friends

The Linux kernel exposes the birth time now for files through statx()
hence make use of it where available. We keep the xattr logic in place
for this however, since only a subset of file systems on Linux currently
expose the birth time. NFS and tmpfs for example do not support it. OTOH
there are other file systems that do support the birth time but might
not support xattrs (smb…), hence make the best of the two, in particular
in order to deal with journal files copied between file system types and
to maintain compatibility with older file systems that are updated to
newer version of the file system.

src/basic/missing.h

@@ -34,10 +34,12 @@
 #include <linux/neighbour.h>
 #include <linux/oom.h>
 #include <linux/rtnetlink.h>
+#include <linux/stat.h>
 #include <net/ethernet.h>
 #include <stdlib.h>
 #include <sys/resource.h>
 #include <sys/socket.h>
+#include <sys/stat.h>
 #include <sys/syscall.h>
 #include <uchar.h>
 #include <unistd.h>
@@ -1372,4 +1374,43 @@ struct fib_rule_uid_range {
 #define PF_KTHREAD 0x00200000
 #endif
 
+#if ! HAVE_STRUCT_STATX
+struct statx_timestamp {
+        int64_t tv_sec;
+        uint32_t tv_nsec;
+        uint32_t __reserved;
+};
+struct statx {
+        uint32_t stx_mask;
+        uint32_t stx_blksize;
+        uint64_t stx_attributes;
+        uint32_t stx_nlink;
+        uint32_t stx_uid;
+        uint32_t stx_gid;
+        uint16_t stx_mode;
+        uint16_t __spare0[1];
+        uint64_t stx_ino;
+        uint64_t stx_size;
+        uint64_t stx_blocks;
+        uint64_t stx_attributes_mask;
+        struct statx_timestamp stx_atime;
+        struct statx_timestamp stx_btime;
+        struct statx_timestamp stx_ctime;
+        struct statx_timestamp stx_mtime;
+        uint32_t stx_rdev_major;
+        uint32_t stx_rdev_minor;
+        uint32_t stx_dev_major;
+        uint32_t stx_dev_minor;
+        uint64_t __spare2[14];
+};
+#endif
+
+#ifndef STATX_BTIME
+#define STATX_BTIME 0x00000800U
+#endif
+
+#ifndef AT_STATX_DONT_SYNC
+#define AT_STATX_DONT_SYNC 0x4000
+#endif
+
 #include "missing_syscall.h"