[Toybox] [PATCH] Fix uptime.c to build when CFG_TOYBOX_UTMPX is false.

[enh]

Fix uptime.c to build when CFG_TOYBOX_UTMPX is false.

The alternative is to provide dummy setutxent, getutxent, endutxent,
struct utmpx, and USER_PROCESS in portability.h, but that seems more
distasteful (and is the reason bionic is unlikely to ever have
<utmpx.h>).

Note that there's an equivalent problem with CFG_TOYBOX_SHADOW, but
Android doesn't build the affected toybox commands because they're
useless on Android for the same reason Android doesn't have
<shadow.h>: our concept of user is fundamentally different.

diff --git a/toys/other/uptime.c b/toys/other/uptime.c
index 91887df..a0e7831 100644
--- a/toys/other/uptime.c
+++ b/toys/other/uptime.c
@@ -34,10 +34,12 @@ void uptime_main(void)
   time(&tmptime);
   now = localtime(&tmptime);

+#if CFG_TOYBOX_UTMPX
   // Obtain info about logged on users
   setutxent();
   while ((entry = getutxent())) if (entry->ut_type == USER_PROCESS) users++;
   endutxent();
+#endif

   // Time
   xprintf(" %02d:%02d:%02d up ", now->tm_hour, now->tm_min, now->tm_sec);