[clang] [Clang] Fix name lookup for dependent bases (PR #114978)

[Vladislav Belov via cfe-commits]

vbe-sc wrote:

```c++
void CXXMethodDecl::addOverriddenMethod(const CXXMethodDecl *MD) {
  assert(MD->isCanonicalDecl() && "Method is not canonical!");
  assert(!MD->getParent()->isDependentContext() &&
         "Can't add an overridden method to a class template!");
```

It seems to me that the second assertion is not really a requirement. @mizvekov , can you please comment on this statement?

https://github.com/llvm/llvm-project/pull/114978