This patch prevents the CFG simplification pass from sinking indirect
calls. Currently, the indirect calls will be combined into a single
indirect call after the arguments have been selected. This prevents the
indirect calls from being replaced with direct ones once the callee is
known through other optimizations.
An example of this is shown in https://godbolt.org/z/jTcfYnvYx where the
indirect calls cannot be replaced with direct calls once they are
inlined and the calls are known. This is generally more costly than
calling the function directly.