[clang] Remove intrusive reference count from `DiagnosticOptions` (#139584)

The `DiagnosticOptions` class is currently intrusively
reference-counted, which makes reasoning about its lifetime very
difficult in some cases. For example, `CompilerInvocation` owns the
`DiagnosticOptions` instance (wrapped in `llvm::IntrusiveRefCntPtr`) and
only exposes an accessor returning `DiagnosticOptions &`. One would
think this gives `CompilerInvocation` exclusive ownership of the object,
but that's not the case:

```c++
void shareOwnership(CompilerInvocation &CI) {
  llvm::IntrusiveRefCntPtr<DiagnosticOptions> CoOwner = &CI.getDiagnosticOptions();
  // ...
}
```

This is a perfectly valid pattern that is being actually used in the
codebase.

I would like to ensure the ownership of `DiagnosticOptions` by
`CompilerInvocation` is guaranteed to be exclusive. This can be
leveraged for a copy-on-write optimization later on. This PR changes
usages of `DiagnosticOptions` across `clang`, `clang-tools-extra` and
`lldb` to not be intrusively reference-counted.

1 files changed, 2 insertions, 2 deletions

diff --git a/clang/lib/Rewrite/HTMLRewrite.cpp b/clang/lib/Rewrite/HTMLRewrite.cpp
index c75835d..1829a4f 100644
--- a/clang/lib/Rewrite/HTMLRewrite.cpp
+++ b/clang/lib/Rewrite/HTMLRewrite.cpp
@@ -636,8 +636,8 @@ static void HighlightMacrosImpl(
   // Temporarily change the diagnostics object so that we ignore any generated
   // diagnostics from this pass.
   DiagnosticsEngine TmpDiags(PP.getDiagnostics().getDiagnosticIDs(),
-                             &PP.getDiagnostics().getDiagnosticOptions(),
-                      new IgnoringDiagConsumer);
+                             PP.getDiagnostics().getDiagnosticOptions(),
+                             new IgnoringDiagConsumer);
 
   // FIXME: This is a huge hack; we reuse the input preprocessor because we want
   // its state, but we aren't actually changing it (we hope). This should really