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

[Henrich Lauko via cfe-commits]

================
@@ -18,12 +18,18 @@
 namespace clang {
 class ASTContext;
 }
+
+namespace cir {
+class LowerModule;
+}
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xlauko wrote:

Nothing in the file uses this?

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