Hello, Since UTMPX_FILE is already defined I figure its W counterpart might as well be defined.
>From a logical standpoint, updwtmpx(3) and utmpxname(3) requires the path to the wtmp file as an argument, but the location of wtmp is non-standard and varies by platform. Some packages use WTMPX_FILE as the "portable" definition of this path. >From a practical standpoint, the OpenSSH package relies on the presence of this #define to enable its wtmpx update code during its build configuration phase, and its wtmpx update code passes WTMPX_FILE as the first argument to updwtmpx(3). Despite their appearance the (U|W)TMPX_FILE macros may not be GNU-isms. It looks like they were added to glibc for compatibility with some *nix flavors. I found some references in some unexpected places, such as SCO Unix  which puts them in /etc, and SGI Irix  which puts them in /var/adm. Here's a patch for your consideration: --- utmps-0.1.0.0/src/include/utmps/utmpx.h 2020-12-28 11:33:23.000000000 +0100 +++ utmps-0.1.0.0/src/include/utmps/utmpx.h.new 2021-04-10 07:50:25.454249526 +0200 @@ -67,8 +67,9 @@ #define UT_NAMESIZE UTMPS_UT_NAMESIZE #define UT_HOSTSIZE UTMPS_UT_HOSTSIZE -/* Unused, but some packages (ex: procps-ng) require this macro to be present */ +/* Unused, but some packages (ex: procps-ng) require these macros to be present */ #define UTMPX_FILE "/run/utmps/utmp" +#define WTMPX_FILE "/run/utmps/wtmp" /* More old GNU/crap compatibility */ #define ut_name ut_user -- Other than that OpenSSH builds and works fine (on Linux-musl) with utmps without any code change on either side.  <http://osr507doc.sco.com/en/man/html.F/utmpx.F.html>  <https://nixdoc.net/man-pages/IRIX/man4/utmpx.4.html>