Add a HowToUseLLJIT example project. A very minimal demo of how to use the LLJIT class, along the lines of the old HowToUseJIT example. llvm-svn: 361435
[ORC] Return ExecutorAddrs rather than JITEvaluatedSymbols from LLJIT::lookup. Clients don't care about linkage, and ExecutorAddr is much more ergonomic.