Make sure we call llvm_shutdown in the TCling destruction

[vgvassilev]

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Description

Currently when we destroy ROOT and TCling we do not properly shut down llvm causing the llvm::ManagedStatics to not be handled properly.

Reproducer

N/A

ROOT version

master

Installation method

N/A

Operating system

all

Additional context

No response

[dpiparo]

Just wondering where this shutdown should be here: why should this be in ROOT and not in Cling?

[vgvassilev]

Cling can be used as a library and we should not shut down the entire process on destroying an object from the library. Ideally this should happen in the "DestroyInterpreter" interface of TCling...