libupnp: add large file defines to CFLAGS

libupnp: add large file defines to CFLAGS

This fixes compilation with glibc and uClibc for the included
sample programs as reported by builtbots for e.g. arc target:

-snip-
In file included from ../../upnp/inc/upnp.h:402:0,
                 from common/sample_util.h:49,
                 from common/sample_util.c:42:
../../upnp/inc/FileInfo.h:22:2: error: #error libupnp uses large file support, so users must do that, too
 #error libupnp uses large file support, so users must do that, too
  ^~~~~
Makefile:577: recipe for target 'common/tv_ctrlpt-sample_util.o' failed
-snap-

Signed-off-by: Michael Heimpold <mhei@heimpold.de>