[clang] [CIR] Handle an empty C++ class in x86_64 callconv lowering (PR #214742)

[Erich Keane via cfe-commits]

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@@ -143,6 +143,10 @@ def CIR_RecordLayoutAttr : CIR_Attr<"RecordLayout", "record_layout", [
     - `record_align_in_bytes`: from `ASTRecordLayout::getAlignment()`.
       Needed because CIR's DataLayout cannot account for
       `__attribute__((aligned(N)))`.
+    - `is_empty`: whether the record carries no data for argument passing
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erichkeane wrote:

Design wise, should we be doing this as calculation? It would seem to me that this is a calculatable condition of "are all fields padding".

https://github.com/llvm/llvm-project/pull/214742