[clang] [CIR] Upstream minimal builtin function call support (PR #142981)

[Andy Kaylor via cfe-commits]

================
@@ -1858,6 +1858,40 @@ def FuncOp : CIR_Op<"func", [
   let hasVerifier = 1;
 }
 
+//===----------------------------------------------------------------------===//
+// LLVMIntrinsicCallOp
+//===----------------------------------------------------------------------===//
+
+def LLVMIntrinsicCallOp : CIR_Op<"llvm.intrinsic"> {
+  let summary = "Call to llvm intrinsic functions that is not defined in CIR";
+  let description = [{
+    The `cir.llvm.intrinsic` operation represents a call-like expression which has
+    a return type and arguments that map directly to an llvm intrinsic.
+    It only records its own name (`intrinsic_name`).
----------------
andykaylor wrote:

I think the answer is in this comment:

```
    // cir::LLVMIntrinsicCallOp expects intrinsic name to not have prefix
    // "llvm." For example, `llvm.nvvm.barrier0` should be passed as
    // `nvvm.barrier0`.
```

https://github.com/llvm/llvm-project/pull/142981