Latest version of ocarina does not parse it by default

mantis #870

Ocarina does not generate the generated-activity.ad? files anymore when
there are no ports in the system

for sync calls

This reverts commit 0ad7c8f3.

use char_array from Interfaces.C when sending a string to C
this avoids issues on 64 bits architectures when passing an Ada 'Length
attribute (32 bits) to a size_t (64 bits) recipient in C