[clang] [Clang] Warn when an explicit alignment is weakened by other directives (PR #198417)

[David Meng via cfe-commits]

davidmenggx wrote:

@AaronBallman Got it, I've added a new note and updated the test cases accordingly. Lmk how this looks, thanks!

https://github.com/llvm/llvm-project/pull/198417