If PolicyKit (polkit-gobject-1 pkg-config package) is not available configure succeeds but the build then fails in defaults/ directory.

The configure code

HAVE_POLKIT=no
AC_ARG_ENABLE(defaults_service,
  AS_HELP_STRING([--enable-defaults-service],
    [build the defaults DBus service @<:@default=auto@:>@]),
  , enable_defaults_service=auto)

if test "x$enable_defaults_service" != "xno" ; then
  PKG_CHECK_MODULES(DEFAULTS, glib-2.0 gobject-2.0 dbus-1 dbus-glib-1 polkit-gobject-1, HAVE_POLKIT=yes, HAVE_POLKIT=no)
  if test "x$HAVE_POLKIT" = "xno"; then
    if test "x$enable_defaults_service" = "xyes" ; then
      AC_MSG_ERROR([[*** Could not find PolicyKit.]])
    fi
  else
    enable_defaults_service=yes
  fi
fi

if test "x$enable_defaults_service" != "xno" ; then
  AC_DEFINE(ENABLE_DEFAULTS_SERVICE, 1, [enable defaults DBus service])
fi

decides it should ENABLE_DEFAULTS_SERVICES even in the absence of polkit-gobject-devel.

The reason is as follows:

enable_defaults_service=auto        # the default from AC_ARG_ENABLE
PKG_CHECK_MODULES(DEFAULTS, ...)    # fails due to missing polkit-gobject-1
HAVE_POLKIT=no                      # set as result
test "x$HAVE_POLKIT" = "xno"        # suceeds
### here still enable_defaults_services=auto
test "x$enable_defaults_service" = "xyes"   # fails, so no error printed
test "x$enable_defaults_service" != "xno"   # succeds, so we build in defaults/

The fix is to make sure enable_defaults_service is either "yes" or "no" after the PKG_CHECK_MODULES() check, not "auto".