invalidMode function
Handles invalid compilation mode by displaying error and usage information.
This function is called when an unrecognized compilation mode is provided as a command line argument. It prints an error message, shows usage instructions, and returns a default compilation mode.
Returns: CompileModes.ASM as a fallback compilation mode.
Implementation
CompileModes invalidMode(){
print("Invalid mode");
printUsage();
return CompileModes.ASM;
}