[clang] [CIR] Upstream CreateOp for ComplexType with folder (PR #143192)

[Henrich Lauko via cfe-commits]

================
@@ -2226,4 +2226,36 @@ def VecTernaryOp : CIR_Op<"vec.ternary",
   let hasVerifier = 1;
 }
 
+//===----------------------------------------------------------------------===//
+// ComplexCreateOp
+//===----------------------------------------------------------------------===//
+
+def ComplexCreateOp : CIR_Op<"complex.create", [Pure, SameTypeOperands]> {
+  let summary = "Create a complex value from its real and imaginary parts";
+  let description = [{
+    The `cir.complex.create` operation takes two operands that represent the
+    real and imaginary part of a complex number, and yields the complex number.
+
+    ```mlir
+    %0 = cir.const #cir.fp<1.000000e+00> : !cir.double
+    %1 = cir.const #cir.fp<2.000000e+00> : !cir.double
+    %2 = cir.complex.create %0, %1 : !cir.complex<!cir.double>
----------------
xlauko wrote:

this does not match assemblyFormat
```suggestion
    %2 = cir.complex.create %0, %1 : !cir.double -> !cir.complex<!cir.double>
```

https://github.com/llvm/llvm-project/pull/143192