configure.ac: add support for position-independent executables. can be disabled
drwxr-xr-x - CVSROOT
drwxr-xr-x - citadel
drwxr-xr-x - ctdlphp
drwxr-xr-x - daphne
drwxr-xr-x - gcit
drwxr-xr-x - libCxClient
drwxr-xr-x - shaggy
drwxr-xr-x - webcit
drwxr-xr-x - wincit