[clang-tools-extra] [llvm] New check `misc-header-guard` (PR #177315)

[Baranov Victor via cfe-commits]

vbvictor wrote:

> * Replace `#pragma once` with guard.

Then https://clang.llvm.org/extra/clang-tidy/checks/portability/avoid-pragma-once.html check can probably be replaced with alias to `misc-header-guard` that will always use logic "replace pragma once with guard".

You can probably use bits of `avoid-pragma-once` check in this check by refactoring into util.

https://github.com/llvm/llvm-project/pull/177315