Fix missing defines _PATH_WTMPX/_PATH_UTMPX in musl

Downloaded from
https://cgit.gentoo.org/proj/musl.git/tree/x11-apps/sessreg/files/sessreg-1.1.0-missing_path_wtmpx.patch

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>

diff -Naur sessreg-1.1.0.orig/sessreg.h sessreg-1.1.0/sessreg.h
--- sessreg-1.1.0.orig/sessreg.h	2015-01-20 05:00:27.000000000 +0000
+++ sessreg-1.1.0/sessreg.h	2016-02-23 11:54:42.057000000 +0000
@@ -103,6 +103,13 @@
 # define TTYS_FILE	"/etc/ttys"
 #endif
 
+#ifndef _PATH_WTMPX
+# define _PATH_WTMPX	"/var/log/wtmp"
+#endif
+#ifndef _PATH_UTMPX
+# define _PATH_UTMPX	"/var/log/utmp"
+#endif
+
 #ifndef WTMPX_FILE
 # define WTMPX_FILE	_PATH_WTMPX
 #endif