In real life, this is a non-issue. Even if one piece of software is compromised, you cannot compromise all of the parts of the system so they align perfectly.
For example, someone compromised your C compiler such that it adds a secret login when it compiles UNIX sources, and that it adds the same feature to the compiler code.
You can modify the compiler code to accept Modified C Language. You can then write a transforming program that converts C into MCL. Then you will compile your new compiler code with the compromised compiler. This will give you MCL compiler. It will still contain the backdoor logic. However, that logic will be deemed irrelevant. Any pattern-matching will be useless against your new language, since attackers cannot know in advance which transformations you applied to it.
After that you can get compiler source, apply MCL transformation, compile the result with your compiler, and you will get a "clean" version of C compiler.
"You can then write a transforming program that converts C into MCL. Then you will compile your new compiler code with the compromised compiler. This will give you MCL compiler. It will still contain the backdoor logic. However, that logic will be deemed irrelevant."
If your transformations preserved behavior wouldn't the backdoor still be there?
What does it matter which language the compiler compiles its code in to as long as the behavior remains the same?
The original scheme recognized a particular sequence of code; recognizing particular behavior no matter how it's implemented is in theory equivalent to the halting problem, I think.
