Initial libjit skeleton.

Not currently generating instructions, but most of the flow is right up to
that point. A lot of work required to refactor the emitter, but wanted to
get this checked in.

src/xenia/cpu/llvmbe/llvm_backend.cc

@@ -69,10 +69,6 @@ CodeUnitBuilder* LLVMBackend::CreateCodeUnitBuilder() {
   return NULL;
 }
 
-LibraryLinker* LLVMBackend::CreateLibraryLinker() {
-  return NULL;
-}
-
 LibraryLoader* LLVMBackend::CreateLibraryLoader() {
   return NULL;
 }