Describe the bug
The simple hello example successfully processed by cppfront v0.7.3, but cppfront >v0.8.x emit uncompilable C++ code

To Reproduce
Steps to reproduce the behavior:

1. `main: () = {
   words: std::vector = ( "Alice", "Bob" );
   hello( words[0] );
   hello( words[1] );
   }

hello: (msg: std::string_view) =
std::cout << "Hello, (msg)$!\n";`

2. Command lines including which C++ compiler you are using: cppfront hello.cpp2
3. Expected result - what you expected to happen:
   cppfront v0.7.3 generate: auto hello(cpp2::impl::in<std::string_view> msg) -> void;
4. Actual result/error
   cppfront v0.8.x generate: [[nodiscard]] auto hello(cpp2::impl::in<std::string_view> msg) -> decltype(auto);

gcc error: error: use of ‘decltype(auto) hello(cpp2::impl::in<std::basic_string_view >)’ before deduction of ‘auto’
msvc error: error C3779: 'hello': a function that returns 'decltype(auto)' cannot be used before it is defined

Additional context
Issue can be simply fixed in cpp2 code like this:
hello: (msg: std::string_view) = { std::cout << "Hello, (msg)$!\n"; }
But this is very strange in my opinion.