[LLVM] Fix some Clang-tidy modernize-use-using and Include What You Use warnings; other minor fixes

[Eugene.Zelenko]

Summary

I checked this patch on my own build on RHEL 6. Regressions were OK.

I decided to make review, because my previous changes caused little controversy.

[compnerd]

LGTM with the extra whitespace around the namespace removed.

[Eugene.Zelenko]

Actually Mehdi found that spaces are consistent with examples in LLVM coding standards.

[mehdi_amini]

In D24017#529225, @Eugene.Zelenko wrote:

Actually Mehdi found that spaces are consistent with examples in LLVM coding standards.

With *long* namespace, not small ones though (you mix both here)

[Eugene.Zelenko]

I think it's better to be consistent with spacing.

[mehdi_amini]

In D24017#555893, @Eugene.Zelenko wrote:

I think it's better to be consistent with spacing.

Sure (and I really don't care about that in the end) but:

1. Don't claim you're doing so according to the coding standard, because it is not true.
2. Different context, different rules: consistency is context-sensitive. A rule saying "include spacing for every 'long' namespace" is also consistent.

[shafik]

Should this be closed?