[clang] [clang] Disallow VLA type compound literals (PR #91891)

[Jim M. R. Teichgräber via cfe-commits]

J-MR-T wrote:

> Please be sure to add a release note to clang/docs/ReleaseNotes.rst so users know about the fix.

Oh, sorry, I didn't find anything know how release notes were handled - will do!

A question on that, would you classify this as a breaking change? Technically, it could break the compilation of programs previously compiled with Clang 17 that compile VLA type compound literals, but never execute the code that they're used in; is that enough for it to be listed as a breaking change? If so, would this go under the `C/C++ Language Potentially Breaking Changes` header? Or should I create a new `C Language Potentially Breaking Changes` header, as this does not affect Clang's C++ behavior itself in any way?

PS: I hope multiple commits in this PR are fine, they are squashed at the end anyway, right?


https://github.com/llvm/llvm-project/pull/91891