[clang] [clang-tools-extra] Reapply "[Clang][Sema] Diagnose class member access expressions naming non-existent members of the current instantiation prior to instantiation in the absence of dependent base classes (#84050)" (PR #90152)

[via cfe-commits]

zmodem wrote:

This seems to break the version of libstdc++ we use in our sysroot: (Details on https://crbug.com/338536261)

```
../../build/linux/debian_bullseye_amd64-sysroot/usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/stl_iterator.h:1718:20: error: use 'template' keyword to treat 'operator =' as a dependent template name
 1718 |       return this->operator=<_It, _Sent>(__x);
      |                    ^
1 error generated.
```

Is that expected, and if so do you have any suggestions for how to work around it?

https://github.com/llvm/llvm-project/pull/90152