Use clang-format-5.0 instead of clang-format-3.8 for the code's style.

Use a newer version of the clang-format tool to format the code. Changes are minor but there is an improved handling of comments directly preceding an #ifdef.

@pdraper I just assigned this to you in case you had some more improvement suggestions on this front.

All looks fine to me. I've built llvm/5.0.2 on COSMA4/5/6 and tested with that. It gave the same results.

Great. So I guess we can go ahead.

merged

mentioned in commit 8f63a644