[clang-tools-extra] [clang-tidy] Add avoid-pragma-once. (PR #140388)

[Baranov Victor via cfe-commits]

================
@@ -0,0 +1,12 @@
+.. title:: clang-tidy - portability-avoid-pragma-once
+
+portability-avoid-pragma-once
+=============================
+
+This check catches pragma once usage.
+
----------------
vbvictor wrote:

It will be very helpful for users to if you write a small description why `pragma once` should be avoided and who may benefit from this (key points from discussion in the issue may be enough). Look at other portability checks description for reference.



https://github.com/llvm/llvm-project/pull/140388