Auto merge of #134740 - Flakebi:amdgpu-target, r=workingjubilee

Add amdgpu target

Add amdgpu target to rustc and enable the LLVM target.

Fix compiling `core` with the amdgpu:
The amdgpu backend makes heavy use of different address spaces. This
leads to situations, where a pointer in one addrspace needs to be casted
to a pointer in a different addrspace. `bitcast` is invalid for this
case, `addrspacecast` needs to be used.

Fix compilation failures that created bitcasts for such cases by
creating pointer casts (which creates an `addrspacecast` under the hood)
instead.

MCP: https://github.com/rust-lang/compiler-team/issues/823
Tracking issue: #135024
Kinda related to the original amdgpu tracking issue #51575 (though that one has been closed for a while).

compiler/rustc_target/src/spec/mod.rs

@@ -1934,6 +1934,8 @@ supported_targets! {
 
     ("nvptx64-nvidia-cuda", nvptx64_nvidia_cuda),
 
+    ("amdgcn-amd-amdhsa", amdgcn_amd_amdhsa),
+
     ("xtensa-esp32-none-elf", xtensa_esp32_none_elf),
     ("xtensa-esp32-espidf", xtensa_esp32_espidf),
     ("xtensa-esp32s2-none-elf", xtensa_esp32s2_none_elf),