Reapply and patch "[CIR][ABI] Apply CC lowering pass by default (#842)" (#944)

This reverts commit 8f699fd and fixes some issues, namely:
 
- CC lowering pass will no longer fail if the function has no AST
information that won't be used.
- Fixed CC lowering not disabling when running certain `cc1` compilation
commands.
- CC lowering can now be disabled when calling `cir-opt` and
`cir-translate`.
- Compilation commands that generate Object files should now invoke CC
lowering by default.

Author: sitio-couto

clang/include/clang/CIR/Dialect/Passes.h

@@ -43,7 +43,7 @@ std::unique_ptr<Pass> createGotoSolverPass();
 /// Create a pass to lower ABI-independent function definitions/calls.
 std::unique_ptr<Pass> createCallConvLoweringPass();
 
-void populateCIRPreLoweringPasses(mlir::OpPassManager &pm);
+void populateCIRPreLoweringPasses(mlir::OpPassManager &pm, bool useCCLowering);
 
 //===----------------------------------------------------------------------===//
 // Registration

clang/include/clang/CIR/LowerToLLVM.h

@@ -29,10 +29,9 @@ class ModuleOp;
 namespace cir {
 
 namespace direct {
-std::unique_ptr<llvm::Module>
-lowerDirectlyFromCIRToLLVMIR(mlir::ModuleOp theModule,
-                             llvm::LLVMContext &llvmCtx,
-                             bool disableVerifier = false);
+std::unique_ptr<llvm::Module> lowerDirectlyFromCIRToLLVMIR(
+    mlir::ModuleOp theModule, llvm::LLVMContext &llvmCtx,
+    bool disableVerifier = false, bool disableCCLowering = false);
 }
 
 // Lower directly from pristine CIR to LLVMIR.