Not good choices for key words.
However, if you tried something like asigning a variable to a c++ codeword that is NOT a c code word would work on a c compiler, but not a c++ one. For example, if you tried to use a codeword like public, private, reinterpret_cast, volatile, extern, etc; the compilation would fail.
Of course, I don't know why we are even having this conversation since glest is coded in C++, not c (NOTHING is coded in c these days...)