[clang-tools-extra] [clang-doc] Refactor error handling to use ExitOnError (PR #141699)

[Paul Kirth via cfe-commits]

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@@ -300,7 +297,7 @@ Example usage for a project using a compile commands database:
                       "these files and continue:\n"
                    << toString(std::move(Err)) << "\n";
     else {
-      llvm::errs() << toString(std::move(Err)) << "\n";
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ilovepi wrote:

I wonder if we should use a lambda or helper function to let us just have a call to `ExitOnErr`. Internally, the helper could call execute and only return an error if `IgnoreMappingFailures == false`. It can still log things, but the usage here would  just be `ExitOnErr(helper(Executor->get->execute(...)))`. WDYT?

https://github.com/llvm/llvm-project/pull/141699