configure.ac states:

  if test "x$with_context_manager" = "xconnman"; then
          PKG_CHECK_MODULES(CONNMAN, connman >= 0.80)
  fi

While at a first glance there's nothing immediately wrong with this, if you read connman.pc you'd notice that this file is meant to be used when building connman plugins. For this reason, it is installed in arch-specific pkg-config dir ($libdir/pkgconfig). Since connman can use plugins built for a single ABI only, on multilib systems connman.pc lands only in lib64 or the equivalent.

The gupnp connman code uses only connman's dbus interface, and therefore is not interested in plugin building details. Therefore multilib build of gupnp could use connman backend on every ABI. However, since connman.pc is installed for native ABI only, the configure check fails and prevents e.g. 32-bit gupnp from using connman.

Please consider removing the check or replacing it with something less fragile. I will also report a bug to connman upstream suggesting that the .pc file is misleading.