Compilation broken on systems without <sys/un.h>

Looking into #1770 (closed) I noticed that on systems without <sys/un.h> (ISC_PLATFORM_HAVESYSUNH undefined), the compilation fails with:

ssu_external.c: In function ‘ux_socket_connect’:
ssu_external.c:59:31: warning: unused parameter ‘path’ [-Wunused-parameter]
   59 | ux_socket_connect(const char *path) {
      |                   ~~~~~~~~~~~~^~~~

getaddrinfo.c: In function ‘get_local’:
getaddrinfo.c:1243:32: error: invalid application of ‘sizeof’ to incomplete type ‘struct sockaddr_un’
 1243 |  ai = ai_alloc(AF_LOCAL, sizeof(*slocal));
      |                                ^
getaddrinfo.c:1249:16: error: invalid use of undefined type ‘struct sockaddr_un’
 1249 |  strlcpy(slocal->sun_path, name, sizeof(slocal->sun_path));
      |                ^~
getaddrinfo.c:1249:47: error: invalid use of undefined type ‘struct sockaddr_un’
 1249 |  strlcpy(slocal->sun_path, name, sizeof(slocal->sun_path));
      |                                               ^~

I don't know what operating systems might be affected, probably none (even Solaris 10 has it), one can "emulate" it like this and rebuild with autoreconf -fi:

--- a/configure.ac
+++ b/configure.ac
@@ -1799,9 +1799,9 @@ AS_IF([test "$enable_linux_caps" = "yes"],
 AC_SUBST([LIBCAP_LIBS])
 
 AC_CHECK_HEADERS(sys/un.h,
-ISC_PLATFORM_HAVESYSUNH="#define ISC_PLATFORM_HAVESYSUNH 1"
-,
 ISC_PLATFORM_HAVESYSUNH="#undef ISC_PLATFORM_HAVESYSUNH"
+,
+ISC_PLATFORM_HAVESYSUNH="#define ISC_PLATFORM_HAVESYSUNH 1"
 )
 AC_SUBST(ISC_PLATFORM_HAVESYSUNH)

I tried for a short while and followed the compiler in fixing warnings and disabling code with #ifdef ISC_PLATFORM_HAVESYSUNH but I end up with either failing tsiggss system test or crashing named.