[ORC] Verify modules when running LLLazyJIT in LLI, and deal with fallout.

The verifier identified several modules that were broken due to incorrect
linkage on declarations. To fix this, CompileOnDemandLayer2::extractFunction
has been updated to change decls to external linkage.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@336150 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed