[clang] [clang] Emit bad shift warnings (PR #70307)

[Aaron Ballman via cfe-commits]

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@@ -277,7 +277,9 @@ void dr258(void) {
 void dr261(void) {
   /* This is still an integer constant expression despite the overflow. */
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AaronBallman wrote:

Probably good to update this comment to mention "extension".

https://github.com/llvm/llvm-project/pull/70307