Assertion failure due to illegal implicit addrspacecast

With https://github.com/JuliaLang/julia/pull/53687, ExaTron.jl tests run into an assertion failure due to what I think is a bug in AMDGPU.jl. The problem lies with free!(AMDGPU.Device.HostCallHolder), which compiles the following ccall:

Expr(:foreigncall, Expr(:call, Core.tuple, :(:hipHostFree), AMDGPU.HIP.libhip), AMDGPU.HIP.hipError_t, svec(Ptr{Nothing}), 0, :(:ccall), SSAValue(7), SSAValue(7))

Here, hipHostFree is invoked with a Ptr{Nothing}) (i.e. addrspace(0)) pointer, however, HostCallHolder contains HostCall which results in passing a LLVMPtr{UInt8, AS.Global} (i.e. addrspace(1)) pointer. This kind of implicit address space conversion is illegal, and only happened to work because of the implicit ptrtoint/inttoptr that happened at the ccall boundary because of Julia storing pointers as i64. That is changing in https://github.com/JuliaLang/julia/pull/53687.

It seems like the HostCall struct shouldn't be used as such on the CPU, where it should simply use a Ptr instead.

Start with free!(AMDGPU.Device.HostCallHolder), the HostCall type, and the ccall expression shown in the issue; compare the pointer address spaces used on CPU and GPU paths. Reproduce the assertion with the ExaTron.jl tests and use the linked failure log to confirm the illegal implicit addrspacecast is gone.