[clang] [flang] [flang][Driver] Support -gsplit-dwarf. (PR #160540)

[Tarun Prabhu via cfe-commits]

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@@ -898,7 +898,19 @@ static void generateMachineCodeOrAssemblyImpl(clang::DiagnosticsEngine &diags,
   llvm::CodeGenFileType cgft = (act == BackendActionTy::Backend_EmitAssembly)
                                    ? llvm::CodeGenFileType::AssemblyFile
                                    : llvm::CodeGenFileType::ObjectFile;
-  if (tm.addPassesToEmitFile(codeGenPasses, os, nullptr, cgft)) {
+  std::unique_ptr<llvm::ToolOutputFile> DwoOS;
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tarunprabhu wrote:

Variable naming in flang is stricter about use of camel-case than clang. Is the capital D here significant enough to justify an exception?

```suggestion
  std::unique_ptr<llvm::ToolOutputFile> dwoOS;
```

https://github.com/llvm/llvm-project/pull/160540