[clang] [CIR] Add handling for volatile loads and stores (PR #156124)

[Henrich Lauko via cfe-commits]

================
@@ -416,18 +420,26 @@ def CIR_LoadOp : CIR_Op<"load", [
     // Load address from memory at address %0. %3 is used by at least one
     // operation that dereferences a pointer.
     %3 = cir.load deref %0 : !cir.ptr<!cir.ptr<i32>>
+
+    // Perform a volatile load from address in %0.
+    %4 = cir.load volatile %0 : !cir.ptr<i32>, i32
+
+    // Others
+    %x = cir.load align(16) atomic(seq_cst) %0 : !cir.ptr<i32>, i32
     ```
   }];
 
   let arguments = (ins Arg<CIR_PointerType, "the address to load from",
                            [MemRead]>:$addr,
                        UnitAttr:$isDeref,
                        OptionalAttr<I64Attr>:$alignment,
+                       UnitAttr:$is_volatile,
----------------
xlauko wrote:

`isDeref` should be snake_case to match the rest of `is_` attributes, but that probably for another typo PR.

https://github.com/llvm/llvm-project/pull/156124