In the stack analysis, we used to consider helper functions as indirect
calls. However, the `CPUStateAccessAnalysis` provides us accurate
information about what an helper function does.
This commit transforms calls to helper functions in a series of ABI IR
instructions reading all the input registers of the helper functions and
a series of instructions writing the output registers.
Note that, while this is a serious improvement over considering them
indirect function calls, it's still suboptimal since
`CPUStateAccessAnalysis` doesn't provide us information as fine-grained
as the ABI analysis.
Alessandro Di Federico
2d521285bb