[llvm] [llvm] Use nullptr instead of 0 or NULL (NFC) (PR #165396)

[Kazu Hirata via llvm-commits]

kazutakahirata wrote:

> LGTM
> 
> Do you mind me asking what's the motivation for these tidy up patches? Is there an end goal such as implementing new clang-tidy-like rules for the codebase, or something like that?

Thanks for the review!  No, I don't have a grand goal of setting up rules, but I just like to periodically run clang-tidy partly because we are already pretty clean for many clang-tidy checks.

https://github.com/llvm/llvm-project/pull/165396