[clang] [Clang][AMDGPU] Add a new builtin type for buffer rsrc (PR #94830)

[Shilei Tian via cfe-commits]

shiltian wrote:

Now `__amdgcn_buffer_rsrc_t` is a 128-bit wide builtin opaque type.

https://github.com/llvm/llvm-project/pull/94830