Allowed SILFunctionType instances for pseudogeneric coroutines without
signatures to be created. Such instances are created by
SILTypeSubstituter::substSILFunctionType when SILGen'ing a conformance
of a pseudogeneric type to a protocol featuring a coroutine requirement.
rdar://81421394
The default C++ object constructor assigns the newly created object out of the function so, it should not return a value. Returning a value will trigger SILGen assertions.
