Makefile: introduce PROG_NAME to contain the 'ct-ng' executable name

With the upcomming --program-{prefix,suffix,transform-name} options,
we'll have a need to centralise the actual executable name, that is
now no longer be a constant.

Rather than spread the prefix/suffix through-out the code, just
centralise the name setting in one place. Beside, transform-name
would not be possible without setting the name at a single location.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

python

import sys

sys.path.insert(0, '@@PREFIX@@/share/gcc-@@VERSION@@/python')

from libstdcxx.v6.printers import register_libstdcxx_printers

register_libstdcxx_printers (None)

end