[ORC] Replace the LLJIT/LLLazyJIT Create methods with Builder utilities.

LLJITBuilder and LLLazyJITBuilder construct LLJIT and LLLazyJIT instances
respectively. Over time these will allow more configurable options to be
added while remaining easy to use in the default case, which for default
in-process JITing is now:

auto J = ExitOnErr(LLJITBuilder.create());

llvm-svn: 359511