[clang] [clang][ExprConst] Support virtual bases in C++26 (PR #204289)

[Yihan Wang via cfe-commits]

================
@@ -669,12 +676,21 @@ class APValue {
     assert(i < getStructNumFields() && "field index OOB");
     return ((StructData *)(char *)&Data)->Elts[getStructNumBases() + i];
   }
+  APValue &getStructVirtualBase(unsigned i) {
+    assert(isStruct() && "Invalid accessor");
+    assert(i < getStructNumVirtualBases() && "base class index OOB");
----------------
yronglin wrote:

```suggestion
    assert(i < getStructNumVirtualBases() && "virtual base index OOB");
```

https://github.com/llvm/llvm-project/pull/204289