Always set errno to a sane value when pututxline(3) fails.

For example, it will now return ESRCH when trying to replace a
nonexistent entry with DEAD_PROCESS.

lib/libc/gen/pututxline.c

@@ -31,6 +31,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/endian.h>
 #include <sys/stat.h>
 #include <sys/uio.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <string.h>
@@ -53,6 +54,7 @@ futx_open(const char *file)
 	/* Safety check: never use broken files. */
 	if (_fstat(fd, &sb) != -1 && sb.st_size % sizeof(struct futx) != 0) {
 		_close(fd);
+		errno = EINVAL;
 		return (NULL);
 	}
 	
@@ -142,6 +144,7 @@ utx_active_remove(struct futx *fu)
 	}
 
 	fclose(fp);
+	errno = ESRCH;
 	return (1);
 }