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

[via llvm-commits]

skc7 wrote:

__attribute__((**cold**)) __global void *
__ockl_dm_alloc(ulong sz){...}

ockl_dm_alloc and ockl_dm_dealloc implementation in device-libs, donot have "used" attribute on them. 
Having "used" attribute is making sure these are not eliminated by compiler passes, and solves the undefined reference issue I'm facing. 

CC: @b-sumner @ampandey-1995 

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