[WIP][CIR] Single-source C++ lowering with ClangIR MLIR CIR #6449

Job	Run time
ubuntu-22.04 llvm assert=ON rtti=ON	4m 25s
ubuntu-22.04 llvm assert=ON rtti=OFF	4m 5s
ubuntu-22.04 llvm assert=OFF rtti=ON	4m 22s
ubuntu-22.04 llvm assert=OFF rtti=OFF	4m 21s
ubuntu-22.04 gcc assert=ON rtti=ON	4m 28s
ubuntu-22.04 gcc assert=ON rtti=OFF	4m 21s
ubuntu-22.04 gcc assert=OFF rtti=ON	3m 54s
ubuntu-22.04 gcc assert=OFF rtti=OFF	4m 3s
ubuntu-24.04 llvm assert=ON rtti=ON	4m 5s
ubuntu-24.04 llvm assert=ON rtti=OFF	4m 18s
ubuntu-24.04 llvm assert=OFF rtti=ON	4m 14s
ubuntu-24.04 llvm assert=OFF rtti=OFF	4m 8s
ubuntu-24.04 gcc assert=ON rtti=ON	3m 48s
ubuntu-24.04 gcc assert=ON rtti=OFF	3m 43s
ubuntu-24.04 gcc assert=OFF rtti=ON	3m 48s
ubuntu-24.04 gcc assert=OFF rtti=OFF	4m 0s
ubuntu-20.04 gcc-11 assert=ON rtti=OFF	4m 46s
ubuntu-20.04 gcc-11 assert=OFF rtti=OFF	4m 36s
ubuntu-20.04 gcc-11 assert=ON rtti=ON	4m 20s
ubuntu-20.04 gcc-11 assert=OFF rtti=ON	4m 35s
windows-2019 msvc assert=ON rtti=ON	6m 25s
windows-2019 msvc assert=ON rtti=OFF	6m 40s
windows-2019 msvc assert=OFF rtti=ON	6m 35s
windows-2019 msvc assert=OFF rtti=OFF	6m 24s
	1h 50m 24s

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