[clang] [clang][bytecode] Make union activation more granular (PR #148835)

[Timm Baeder via cfe-commits]

tbaederr wrote:

Unfortunately some negative impact on compile times: https://llvm-compile-time-tracker.com/compare.php?from=8fb3c271dafd158d36a17212ab609294d725c230&to=51547a1e34c8377d16090930b6af5509dd164a05&stat=instructions:u

https://github.com/llvm/llvm-project/pull/148835