[clang] [llvm] [IR] Make dead_on_return attribute optionally sized (PR #171712)

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github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Linux-->
# :penguin: Linux x64 Test Results

* 168182 tests passed
* 2997 tests skipped
* 88 tests failed

Failed tests and their output was too large to report. Download the build's log file to see the details.

If these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the `infrastructure` label.

https://github.com/llvm/llvm-project/pull/171712