Tests that use the `%target-swift-emit-module-interface` lit substitution are
designed to test the behavior of the compiler when emitting module interfaces
for resilient libraries. It therefore makes sense to pass `-parse-as-library`
by default for these frontend invocations.
Fixes a few tests that were accidentally depending on parsing source files as
top level code.
We might infer internal function labels as `$0` from a closure with which a variable is initialised. But we don’t want to print the function signature as `(_ $0: Int) -> Int` because `$0` is not a valid variable name to declare.
So, in the case described above, only print the type.
Fixes rdar://77462547
