[clang] [clang][AVR] Add basic AVR builtin functions (PR #203214)

[Patryk Wychowaniec via cfe-commits]

Patryk27 wrote:

Hi! I'm getting an error trying to build this 👀 

```
llvm-project/clang/lib/CodeGen/TargetBuiltins/AVR.cpp:16:10: fatal error: 'llvm/IR/IntrinsicsAVR.h' file not found
   16 | #include "llvm/IR/IntrinsicsAVR.h"
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
```

https://github.com/llvm/llvm-project/pull/203214