[BUILD] OpenVDB fails to build with LLVM 18 about openvdb

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What exactly is the problem with opaque pointers in OpenVDB / LLVM 16+ ?

The opaque pointers change is a fundamental design/behaviour change in LLVM. OpenVDB AX will most likely crash using LLVM 16 and probably fail to compile entirely under LLVM 17/18. Most software that uses LLVM will have had to go through a similar transition. There are migration guidelines, but different projects will have different levels of complexity depending on their use of typed pointer components - and we use them a fair amount in AX.

https://llvm.org/docs/OpaquePointers.html

OpenVDB should be compatible with recent stable LLVM releases. LLVM 16 was released two years ago, and the current version is 18.

This is simply a resourcing issue, we haven't had the time to commit to updating. I will do my best to see if I can solve this in the short term but unfortunately can't make any deadline promises.