[clang] [clang] Implement C2y stdc_memreverse8 and stdc_memreverse8u{8,16,32,64} builtins (PR #197358)

[Aaron Ballman via cfe-commits]

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@@ -3863,6 +3863,18 @@ Sema::CheckBuiltinFunctionCall(FunctionDecl *FDecl, unsigned BuiltinID,
       return ExprError();
     break;
 
+  case Builtin::BI__builtin_stdc_memreverse8:
+  case Builtin::BIstdc_memreverse8u8:
+  case Builtin::BIstdc_memreverse8u16:
+  case Builtin::BIstdc_memreverse8u32:
+  case Builtin::BIstdc_memreverse8u64:
+    if (Context.getTargetInfo().getCharWidth() != 8) {
+      Diag(TheCall->getBeginLoc(), diag::err_builtin_requires_char_bit_8)
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AaronBallman wrote:

I agree with the code but I also don't think we have a way to test it either; we don't have options to let you control `CHAR_BIT` and we don't have targets that aren't 8-bit currently.

https://github.com/llvm/llvm-project/pull/197358