[clang] Fix memcpy-operator= generation with restrict parameters. (PR #194906)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

I'm still trying to think through the ramifications of this. I think it's roughly correct, but there are a lot of other qualifiers (and type attributes, etc). I did notice we seem to be handling `volatile` incorrectly: https://godbolt.org/z/soGb7q1a1 (we lower to a memcpy but that fails to meet the requirement that we do the volatile loads and stores). You mention address spaces, and that's true for `__attribute__((address_space))` but what about things like `__constant` in OpenCL/CUDA/SYCL, etc; those have different rules despite also being address spaces.

https://github.com/llvm/llvm-project/pull/194906