[clang] [CIR][NFC] Generate ABI lowering patterns with TableGen (PR #175021)

[Andy Kaylor via cfe-commits]

================
@@ -79,6 +79,8 @@ class LLVMLoweringInfo {
 
 class CIR_Op<string mnemonic, list<Trait> traits = []> :
     Op<CIR_Dialect, mnemonic, traits>, LLVMLoweringInfo {
+  // Should we generate an ABI lowering pattern for this op?
+  bit hasAbiLowering = false;
----------------
andykaylor wrote:

```suggestion
  bit hasCXXABILowering = false;
```
I expect to have multiple lowering passes related to ABI, one for the C++ ABI, one for calling-convention-related ABI, and at least one for other things. I think it makes sense to keep these separate. At the very least, I would like the calling convention handling to be dialect agnostic.

https://github.com/llvm/llvm-project/pull/175021