This additional check allows, e.g. for using Clang as C compiler while
using g++ as the C++ compiler. (Clang has better error checking and
messages, plus compiles faster).
git-svn-id: https://warzone2100.svn.sourceforge.net/svnroot/warzone2100/trunk@10167 4a71c877-e1ca-e34f-864e-861f7616d084