prefer login_getpwclass() to login_getclass()

FreeBSD has login_getpwclass() that does some special magic for
UID=0. Prefer this to login_getclass() as its easier to emulate
the former with the latter.

Based on FreeBSD PR 37416 via Ed Maste; ok dtucker@

auth.c

@@ -604,7 +604,7 @@ getpwnamallow(struct ssh *ssh, const char *user)
 	if (!allowed_user(ssh, pw))
 		return (NULL);
 #ifdef HAVE_LOGIN_CAP
-	if ((lc = login_getclass(pw->pw_class)) == NULL) {
+	if ((lc = login_getpwclass(pw)) == NULL) {
 		debug("unable to get login class: %s", user);
 		return (NULL);
 	}

configure.ac

@@ -1841,6 +1841,7 @@ AC_CHECK_FUNCS([ \
 	llabs \
 	localtime_r \
 	login_getcapbool \
+	login_getpwclass \
 	md5_crypt \
 	memmem \
 	memmove \

openbsd-compat/openbsd-compat.h

@@ -48,6 +48,10 @@
 #include "blf.h"
 #include "fnmatch.h"
 
+#if defined(HAVE_LOGIN_CAP) && !defined(HAVE_LOGIN_GETPWCLASS)
+# define login_getpwclass(pw) login_getclass(pw->pw_class)
+#endif
+
 #ifndef HAVE_BASENAME
 char *basename(const char *path);
 #endif