[CMake] Give program path of data directory at installation time

[Jordi Gutiérrez Hermoso]

I have a Python script $program that should be installed under bin/,
but it needs a lot of data that should be installed under
share/$program/. I would like for the install Makefile target to
somehow modify $program to let it know the absolute pathname of where
the data share/$program/ is, including perhaps any $DESTDIR. How
should I make my program aware of where the data was installed?

If there is a different way altogether that you can think of (have
$program read configuration files from /etc?), please suggest it.

TIA,
- Jordi G. H.