[llvm] [Support] Extend ExtensibleRTTI utility to support basic multiple inheritance. (PR #112643)

[Lang Hames via llvm-commits]

lhames wrote:

The motivating use-case is ORC memory management: We want `JITLinkMemoryManager`s to be able to inherit from additional interfaces (e.g. for allocating contiguous address ranges for each JITDylib), and to be able to check whether a given memory manager supports a given extended interface.

https://github.com/llvm/llvm-project/pull/112643