[opaque pointer type] gep API migration, ArgPromo
[opaque pointer type] gep API migration, ArgPromo

This involved threading the type-to-gep through a data structure, since
the code was relying on the pointer type to carry this information. I
imagine there will be a lot of this work across the project... slow
work chasing each use case, but the assertions will help keep me honest.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@232277 91177308-0d34-0410-b5e6-96231b3b80d8

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