[clang] [Format] Configure ASSIGN_OR_RETURN macros for Google style (PR #169037)

[Ilya Biryukov via cfe-commits]

ilya-biryukov wrote:

> Please note that user-added Macros will overwrite the default:

This looks odd, but also outside of the scope of this PR; changing the behavior for parsing clang-format configurations looks like something that would have a much bigger blast radius than this PR.

But let me know if you expect something concrete from this PR to workaround it.

https://github.com/llvm/llvm-project/pull/169037