[clang] [clang-tools-extra] [lldb] [clang] Remove intrusive reference count from `DiagnosticOptions` (PR #139584)

[Kazu Hirata via cfe-commits]

kazutakahirata wrote:

@jansvoboda11 I also see:

```
clang-tools-extra/clang-tidy/plugin/ClangTidyPlugin.cpp:45:51: error: too few arguments to function call, expected 2, have 1
   45 |     Context->setDiagnosticsEngine(DiagEngine.get());
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~                 ^
```

Another one:

```
clang/include/clang/Frontend/LogDiagnosticPrinter.h:54:22: error: private field 'DiagOpts' is not used [-Werror,-Wunused-private-field]             
   54 |   DiagnosticOptions &DiagOpts;                                                                                                                                                                
      |                      ^                                                                                                                                                                        
````

from `clang/lib/Frontend/LogDiagnosticPrinter.cpp`.

```
llvm/include/llvm/ADT/IntrusiveRefCntPtr.h:163:37: error: no member named 'Retain' in 'clang::DiagnosticOptions'                                    
  163 |   static void retain(T *obj) { obj->Retain(); }                                                                                                                                               
      |                                ~~~  ^                                                                                                                                                         
```

from `flang/lib/Frontend/CompilerInvocation.cpp`.


https://github.com/llvm/llvm-project/pull/139584