This patch adds another flavor of Alias Analysis which
is a variant of the earlier CFLAliasAnalysis.
This analysis is still experimental and is contributed
as an alternative to the two existing similar passes.
Analysis is off by default but enabled by
-mllvm -use-cfl-aa=on-demand -mllvm -use-cfl-aa-in-codegen=on-demand
A summary of approach and experimentation is here:
https://www.facebook.com/notes/david-callahan/llvm-cfl-alias-analysis/10150648030284971