Added a *very* initial cut at a lexicon for LLVM. I don't plan to write

Added a *very* initial cut at a lexicon for LLVM. I don't plan to write
this whole thing. Just use the pattern in the file to add entries as you
think of them. This will be really helpful for newbies to advanced compiler
optimization techniques such as myself.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@15878 91177308-0d34-0410-b5e6-96231b3b80d8