[clang] [CIR][CodeGen] Implement BI__builtin_fpclassify function (PR #183893)

[Andy Kaylor via cfe-commits]

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@@ -1544,8 +1544,70 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
   case Builtin::BI__builtin_isinf_sign:
   case Builtin::BI__builtin_flt_rounds:
   case Builtin::BI__builtin_set_flt_rounds:
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andykaylor wrote:

```suggestion
  case Builtin::BI__builtin_set_flt_rounds:
    return errorBuiltinNYI(*this, e, builtinID);
```
You need this to prevent fall through.

https://github.com/llvm/llvm-project/pull/183893