Add -misc-use-anonymous-namespace to .clang-tidy

This is at odds with the coding standard.
Quoting https://llvm.org/docs/CodingStandards.html#anonymous-namespaces
> Because of this, we have a simple guideline: make anonymous namespaces
> as small as possible, and only use them for class declarations.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D149664