[clang] [CIR] Add TargetLowering pass (PR #179245)

[Andy Kaylor via cfe-commits]

================
@@ -83,15 +83,25 @@ def GotoSolver : Pass<"cir-goto-solver"> {
 }
 
 def CXXABILowering : Pass<"cir-cxxabi-lowering", "mlir::ModuleOp"> {
-  let summary = "Lower abstract C++ operations to target-specific ABI form";
+  let summary = "Lower CIR according to ABI requirements";
   let description = [{
-    This pass lowers high-level operations that represent C++ constructs in a
-    target-independent way to concrete, target specific operations.
+    This pass lowers CIR operations and types that represent high-level C/C++
+    constructs to a more "fundamental" form according to the target ABI
----------------
andykaylor wrote:

```suggestion
    constructs to a more fundamental form according to the target ABI
```

https://github.com/llvm/llvm-project/pull/179245