[llvm] [NFC][CodingStandard] Fix text style for C++ keywords (PR #128932)

[Rahul Joshi via llvm-commits]

jurahul wrote:

This fixes the incorrect formatting of keywords (they come out as emphasized) in the current version: https://llvm.org/docs/CodingStandards.html#restrict-visibility

https://github.com/llvm/llvm-project/pull/128932