ZTS: small fix for SEEK_DATA/SEEK_HOLE tests (#16413)

Some libc's like uClibc lag the proper definition of SEEK_DATA
and SEEK_HOLE. Since we have only two files in ZTS which use
these definitons, let's define them by hand:

```
#ifndef SEEK_DATA
#define SEEK_DATA 3
#endif
#ifndef SEEK_HOLE
#define SEEK_HOLE 4
#endif
```

There should be no failures, because:
- FreeBSD has support for SEEK_DATA/SEEK_HOLE since FreeBSD 8
- Linux has it since Linux 3.1
- the libc will submit the parameters unchanged to the kernel

Signed-off-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>

tests/zfs-tests/cmd/mmap_seek.c

@@ -35,6 +35,16 @@
 #include <linux/fs.h>
 #endif
 
+/* some older uClibc's lack the defines, so we'll manually define them */
+#ifdef	__UCLIBC__
+#ifndef	SEEK_DATA
+#define	SEEK_DATA 3
+#endif
+#ifndef	SEEK_HOLE
+#define	SEEK_HOLE 4
+#endif
+#endif
+
 static void
 seek_data(int fd, off_t offset, off_t expected)
 {

tests/zfs-tests/tests/functional/cp_files/seekflood.c

@@ -36,6 +36,13 @@
 #include <sys/stat.h>
 #include <sys/wait.h>
 
+/* some older uClibc's lack the defines, so we'll manually define them */
+#ifdef	__UCLIBC__
+#ifndef	SEEK_DATA
+#define	SEEK_DATA 3
+#endif
+#endif
+
 #define	DATASIZE	(4096)
 char data[DATASIZE];