[CIR][LowerToLLVM] Lowering triple from cir.triple attribute

[seven-mile]

Currently, the final target triple in LLVM IR is set in CIRGenAction, which is not executed by cir tools like cir-translate. This PR delay its assignment to LLVM lowering, enabling sharing the emitting of target triple between different invoking paths.

[seven-mile]

A series of patches will be made to improve the triple and data layout in ClangIR, and this is the first one. The next steps are as follows:

• Remove the redundancy between dlti.dl_spec and llvm.data_layout in CIR, with the LLVM one being removed.
• Depending on the upstream PR llvm-project#116090, add the --target option to cir-translate / cir-opt and relieve us from the horror of manually specifying data layout in our tests.