Update .clang-tidy to drop static -> anonymous namespace warnings

[bondhugula]

Summary

This gets rid of numerous clang-tidy warnings in editor environments
along:

... declared 'static', move to anonymous namespace instead [misc-use-anonymous-namespace]

The MLIR style has been to use 'static' for free-standing functions and
this appears in line with https://llvm.org/docs/CodingStandards.html#namespace-indentation

In any case, these warnings completely pollute/mess up in-editor
diagnostics (for eg. vim with YCM would show all these clang-tidy
warnings making real ones nearly invisible).

[bondhugula]

Fix spacing.

[ftynse]

Thanks, these are quite annoying!

[bondhugula]

Fix syntax.

[mehdi_amini]

Seems like it could one at the top-level? Actually not even clear why clang-tidy has this warning enabled in the LLVM config?

[mehdi_amini]

Seems like not unusual that we hit this kind of issues: https://reviews.llvm.org/D131414 ; please move it on level above :)

[lattner]

+1, I don't know why anyone would prefer anon namespaces to static where static works.

[bondhugula]

I thought I had committed this, but it looks like I missed it, and someone added this to LLVM's .clang-tidy in the meanwhile (on May 2)! Closing.

mlir/.clang-tidy

 InheritParentConfig: true
 Checks: >
         -misc-const-correctness,
+        -misc-use-anonymous-namespace,
         bugprone-argument-comment,
         bugprone-assert-side-effect,
         bugprone-branch-clone,
         bugprone-copy-constructor-init,
         bugprone-dangling-handle,
         bugprone-dynamic-static-initializers,
         bugprone-macro-parentheses,
         bugprone-macro-repeated-side-effects,