[clang] [CIR] Upstream builtin lowering emitter & FAbs op (PR #151750)

[Andy Kaylor via cfe-commits]

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@@ -25,6 +25,7 @@ using namespace clang;
 enum ActionType {
   PrintRecords,
   DumpJSON,
+  GenCIRBuiltinsLowering,
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andykaylor wrote:

All of the changes in this directory need to be guarded by a `CLANG_ENABLE_CIR` preprocessor check, and we'll need approval from the regular clang maintainers.

https://github.com/llvm/llvm-project/pull/151750