We only ever intended to support C++, but the condition we were testing allowed Objective-C++ code by mistake.
A coroutine function body (`CoroutineBodyStmt`) may have null children, which causes `isa` to segfault.
ControlFlowContext
AdornedCFG
This expresses better what the class actually does, and it reduces the number of `Context`s that we have in the codebase. A deprecated alias `ControlFlowContext` is available from the old header.