[cxx-interop] Do not crash when diagnosing cycles for C++ operators
[cxx-interop] Do not crash when diagnosing cycles for C++ operators

C++ operator functions are `NamedDecl`s, but they don't have a trivial name, and calling `getName` results in an assertion failure.

This was discovered during C++ interop adoption in SwiftCompilerSources.

```
Assertion failed: (Name.isIdentifier() && "Name is not a simple identifier"), function getName, file Decl.h, line 277.
...
/Volumes/Projects/swift/llvm-project/clang/include/clang/AST/DependentDiagnostic.h:150:8: importing 'clang::DeclContext::ddiag_iterator::operator=='
```

roambotics/swift,glessard/swift,JGiola/swift,benlangmuir/swift,glessard/swift,roambotics/swift,JGiola/swift,roambotics/swift,glessard/swift,JGiola/swift,apple/swift,apple/swift,JGiola/swift,JGiola/swift,roambotics/swift,glessard/swift,apple/swift,roambotics/swift,glessard/swift,benlangmuir/swift,benlangmuir/swift,roambotics/swift,apple/swift,benlangmuir/swift,apple/swift,JGiola/swift,glessard/swift,benlangmuir/swift,benlangmuir/swift,apple/swift