[llvm] Improve description of what is considered a security issue (PR #147035)

[Kristof Beyls via llvm-commits]

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@@ -204,6 +204,11 @@ The LLVM Security Policy may be changed by majority vote of the LLVM Security Re
 What is considered a security issue?
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+Below, with "security-sensitive", we mean that a discovered bug or vulnerability
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kbeyls wrote:

Thanks, those are better. I ended up going with your first suggestion.

https://github.com/llvm/llvm-project/pull/147035