Where to declare CharUnits wrapper of RoundUpToAlignment()?

I'd like to add a wrapper function for the llvm::RoundUpToAlignment()
function. It would take and return values in CharUnits. Any
recommendations for which header file should hold its declaration?

All of the calls to llvm::RoundUpToAlignment() occur in the CodeGen and
AST libraries, so somewhere in AST seems appropriate. But where? In
ASTContext.h, maybe? Or would a new ASTExtras.h be more appropriate?

-Ken

Why not make it part of CharUnits?

- Daniel