No, you're wrong. The old code will have something like
typedef char bool
And thus compiling this code in C99 would not work if bool were a keyword of the language. That is why the boolean datatype is called _Bool, so it doesn't clash with old code. In new code, you can still use the bool datatype, but instead of defining it yourself with char or int, you should better use a typedef of the _Bool datatype in stdbool.h
Your attitude is rediculous... Let code break! Make sure there is a __c1x macro and maintained projects will take 30 seconds to fix. Unmaintained projects will die, yay!
I will never purchase a compiler made by you or someone who thinks like you. Sure, it will take 30 seconds to fix your puny 2000 line program that's contained in just a handful of files all of which you control and with no code generation engines or text transformation steps in its build chain. But it wouldn't be that easy for everyone.
typedef char bool
And thus compiling this code in C99 would not work if bool were a keyword of the language. That is why the boolean datatype is called _Bool, so it doesn't clash with old code. In new code, you can still use the bool datatype, but instead of defining it yourself with char or int, you should better use a typedef of the _Bool datatype in stdbool.h