[clang] [win][clang] Do not inject static_assert macro definition (PR #147030)

[Corentin Jabot via cfe-commits]

https://github.com/cor3ntin commented:

LGTM but please give @AaronBallman a chance to comment, as this reverts a previous patch of his (which I think was too clever)!

https://github.com/llvm/llvm-project/pull/147030