[clang] [CIR] Upstream support for lowering cir.switch to LLVM (PR #140425)

[Andy Kaylor via cfe-commits]

================
@@ -1038,6 +1038,37 @@ mlir::LogicalResult CIRToLLVMGlobalOpLowering::matchAndRewrite(
   return mlir::success();
 }
 
+mlir::LogicalResult CIRToLLVMSwitchFlatOpLowering::matchAndRewrite(
+    cir::SwitchFlatOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+
+  llvm::SmallVector<mlir::APInt, 8> caseValues;
+  if (op.getCaseValues()) {
+    for (mlir::Attribute val : op.getCaseValues()) {
+      auto intAttr = dyn_cast<cir::IntAttr>(val);
----------------
andykaylor wrote:

```suggestion
      auto intAttr = cast<cir::IntAttr>(val);
```
Make this assert.

https://github.com/llvm/llvm-project/pull/140425