lttng-babeltrace: make sure WCHAR and LARGEFILE are enabled

Since lttng-babeltrace depends on util-linux and libglib2, we need to
make sure WCHAR and LARGEFILE are enabled.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>