[llvm] [Xtensa] Implement Code Density Option. (PR #119639)

[Andrei Safronov via llvm-commits]

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+# RUN: not llvm-mc -triple xtensa --mattr=+density %s 2>&1 | FileCheck %s
+
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andreisfr wrote:

I'm sorry, you mean that we don't need to create specific directory for Xtensa architecture options(extensions) tests in "../MC/Xtensa/"? Or use other directory structure, for example for each option(extension) create correspondence directory "../MC/Xtensa/CodeDensity"?

https://github.com/llvm/llvm-project/pull/119639