[tree-ssa]: INDIRECT_VAR patch badly breaks PTA

[Daniel Berlin]

Your INDIRECT_REF patch has badly broken PTA, and i'm not sure how to fix
it.

You now ask PTA about aliasing between pointers and memory tag variables
(IE variables that don't actually exist in the function).
Because they don't really exist in the function, PTA has no idea
about the variable, and aborts (as it should, since it should have
seen every variable you could query about)

Queries to PTA should be about a pointer and a variable, not a pointer and
a fake variable.

--Dan