What's the relevant definition of "owned" here? As long as Apple can modify LLVM however it wants, and as long as it's sure no corporate actor can restrict access rights to it in the future, it effectively owns it, altough not exclusively.

Having exclusive rights on a strategic business brick is important when this brick is enough to give someone else a stronghold on the whole vertical market. Although having a good compilers is one of the many requirements in Apple's business model, it's neither the defining feature, nor what competitors miss in order to threaten Apple.

So yes, in this context, Apple non-exclusively owns LLVM.