insertvalue and extractvalue to use constant indices instead of
Value* indices. And begin updating LangRef.html.
There's definately more to come here, but I'm checking this
basic support in now to make it available to people who are
interested.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51806 91177308-0d34-0410-b5e6-96231b3b80d8
