[clang] [llvm] [RISCV] Remove experimental from Ztso. (PR #96465)

[Philip Reames via cfe-commits]

preames wrote:

Once https://github.com/llvm/llvm-project/pull/90266 lands with the attributes off by default, I think we should move forward with relanding this.  We do need one change though - our TSO lowering unconditionally uses the A6S ABI variant - right? - so we need to adjust the attribute emission to generate A6S when compiling for TSO.  This is pretty minor honestly, but we should do it.  



https://github.com/llvm/llvm-project/pull/96465