[llvm] [WIP] Separate Asan instrumentation in amdgpu-sw-lower-lds. (PR #134832)

[via llvm-commits]

skc7 wrote:

> If we make those functions used, I think the runtime will end up setting up every kernel for device malloc and there will be performance complaints.

Yeah, that is the downside of always setting the attribute. 
I'm checking ways to set this "used" attribute only when asan is enabled. But I think device-libs would not have the information if asan is enabled or not.

https://github.com/llvm/llvm-project/pull/134832