scanner: Move PROGRAM_NAME define

PROGRAM_NAME was defined within the if block of HAVE_LIBXML, causing a
compilation failure when libxml is not present.

Move the define of PROGRAM_NAME out of the if block.

Signed-off-by: Yong Bakos <ybakos@humanoriented.com>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>