Do not try to use _Static_assert() with C++ code

Reported by Emmet Hikory <persia>

See bug #22323


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@25522 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Increased number of attempts to generate map from two to three.

See patch #4900


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@25523 a0f10bec-cc02-0410-94fc-a9cfff90b4cd