[clang] [CIR] Add undef handling to enable global lambdas (PR #169721)

[Henrich Lauko via cfe-commits]

================
@@ -2046,9 +2054,11 @@ CIRToLLVMGlobalOpLowering::matchAndRewriteRegionInitializedGlobal(
     cir::GlobalOp op, mlir::Attribute init,
     mlir::ConversionPatternRewriter &rewriter) const {
   // TODO: Generalize this handling when more types are needed here.
-  assert((isa<cir::ConstArrayAttr, cir::ConstRecordAttr, cir::ConstVectorAttr,
-              cir::ConstPtrAttr, cir::ConstComplexAttr, cir::GlobalViewAttr,
-              cir::TypeInfoAttr, cir::VTableAttr, cir::ZeroAttr>(init)));
+  assert(
+      (isa<cir::ConstArrayAttr, cir::ConstRecordAttr, cir::ConstVectorAttr,
+           cir::ConstPtrAttr, cir::ConstComplexAttr, cir::GlobalViewAttr,
+           cir::TypeInfoAttr, cir::VTableAttr, cir::UndefAttr, cir::ZeroAttr>(
----------------
xlauko wrote:

```suggestion
           cir::TypeInfoAttr, cir::UndefAttr, cir::VTableAttr, cir::ZeroAttr>(
```

https://github.com/llvm/llvm-project/pull/169721