Linux 6.8 compat: implement strlcpy fallback

Linux has removed strlcpy in favour of strscpy. This implements a
fallback implementation of strlcpy for this case.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Sponsored-by: https://despairlabs.com/sponsor/
Closes #15805

module/os/linux/spl/spl-thread.c

@@ -26,6 +26,7 @@
 #include <sys/thread.h>
 #include <sys/kmem.h>
 #include <sys/tsd.h>
+#include <sys/string.h>
 
 /*
  * Thread interfaces