Previously using defer with an exported function generated an invalid function call due to differences between TinyGo's calling convention and the C calling convention.
This is a common operation:
freevar := ...
defer func() {
println("I am deferred:", freevar)
}()
The function is thus an immediately applied closure. Only this form is
currently supported, support for regular (fat) function pointers should
be trivial to add but is not currently implemented as it wasn't
necessary to get fmt to compile.
