MandatoryPerformanceOptimizations: don't de-virtualize a generic class method call to specialized method
This results in wrong argument/return calling conventions.
First, the method call must be specialized. Only then the call can be de-virtualized.
Usually, it's done in this order anyway, because the `class_method` instruction is located before the `apply`.
But when inlining functions, the order (in the worklist) can be the other way round.
Fixes a compiler crash.
rdar://154631438