Disable concurrent compilation to prevent dangling Module pointers

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Summary

Cling uses a single LLVMContext (SingleThreadedContext) and keeps raw pointers to Modules (Transaction::m_CompiledModule) for later unloading via TransactionUnloader::unloadModule. When concurrent compilation is enabled, LLJIT sets CloneToNewContextOnEmit which clones each Module into a fresh context during materialization, destroying the original. That turns m_CompiledModule into a dangling pointer and crashes in RevertTransaction (use-after-free in the Module's function list).

Fix: Call Builder.setSupportConcurrentCompilation(false) in the IncrementalJIT constructor.

Test plan

• Without this fix, undo() / RevertTransaction crashes with use-after-free
• With the fix, 34/34 tests pass including undo/rollback tests
• Tested on ARM64 Linux and Windows x64