Summary:
Update handling of `OffsetOfExpr` based on the new type definition
from updated version of clang-plugin.
Together with the change to clang-plugin, this essentially fixes hard
crash while analysing C/C++ files with non-literal `offsetof`
expression.
Fixes GH issues [#1178](https://github.com/facebook/infer/issues/1178), [#1212](https://github.com/facebook/infer/issues/1212)
Reviewed By: jvillard
Differential Revision: D20159173
fbshipit-source-id: 65fc228a4