[clang] [Wunsafe-buffer-usage] Address some false positives in handling array indices that are decidably correct (PR #117370)

[Reid Kleckner via cfe-commits]

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@@ -463,6 +471,13 @@ AST_MATCHER(ArraySubscriptExpr, isSafeArraySubscript) {
       return true;
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rnk wrote:

I think getting the integer constant expr is more general, we can remove the IntegerLiteral test here, and if all tests pass, I would consider it functionally equivalent. This code seems like it was tested to a reasonably high standard.

https://github.com/llvm/llvm-project/pull/117370