This patch adds calls to Hexagon-specific passes that can be safely skipped to opt-in to the optimization bisect mechanism.
I selected the passes to be skipped based on the fact that they were not added at CodeGenOpt::None in HexagonTargetMachine.cpp. Based on that criteria, I did not add opt-in calls to the following passes, which appear to be required:
Note that the call to skipFunction() will also check for the "optnone" function attribute, so this can theoretically result in passes being skipped even when optimization bisect is not being done. However, I believe that any pass that can be safely skipped should be skipped for functions with the optnone attribute.
See D19172 for details on the base optimizaton bisect implementation.