[clang] [llvm] [AVR] Handle flash RO data mapped to data space for newer devices (PR #146244)

[Ben Shi via llvm-commits]

benshi001 wrote:

> @benshi001 @Patryk27 Could you review this?

As I have told you several days ago, each functional change requires unit tests, your PR involves 
1. clang driver
2. clang builtin macro
3. avr backend codegen

Each part needs unit tests to show what are affected. 

https://github.com/llvm/llvm-project/pull/146244