Replaces an alloc_stack of an enum by an alloc_stack of the payload if only one enum case (with payload) is stored to that location.
For example:
%loc = alloc_stack $Optional<T>
%payload = init_enum_data_addr %loc
store %value to %payload
...
%take_addr = unchecked_take_enum_data_addr %loc
%l = load %take_addr
is transformed to
%loc = alloc_stack $T
store %value to %loc
...
%l = load %loc
https://bugs.swift.org/browse/SR-12710
