[clang] [clang][AVR] Improve compatibility of inline assembly with avr-gcc (PR #136534)

[Sergei Barannikov via cfe-commits]

s-barannikov wrote:

> > gcc doesn't seem to allow it? https://godbolt.org/z/4zh8TTPac
> 
> avr-gcc allow value 64 for constraint 'I' in very special case, such as #51513.

I guess the test needs to be updated to be representative?

> And my solution is loosen that check in the frontend, but let the AVR backend to deny the illegal constraint value 64.

This deserves a comment in code so that other people don't get confused about this and don't try to change it back to 63.


https://github.com/llvm/llvm-project/pull/136534