This silences some identifier 'concept' is a keyword in C++20 [-Wc++20-compat] warnings when building the Titanic engine with G++ 13.

Small notes:

• The renaming was done with Xcode contextual rename function to be sure not to make any mistake.
• For addConcept() and removeConcept() I'm just using *c as the parameter, since the function itself reads a bit ambiguous otherwise, to me.
• The pet_glyphs.cpp change is for an unused variable.