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>
[Retrieved from:
https://git.buildroot.net/buildroot/tree/package/x11r7/xapp_sessreg/0001-missing_path_wtmpx.patch

]
Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>