The `_stret` API are not included in the ARM64 version of iOS (not
needed) but the removal of `dlsym` cause build failures*
So we're providing dummy symbols, just like what we did for tvOS,
to please the native linker (so nothing is undefined) and keep the
benefits of not using dlsym.
* Xamarin.iOS.dll (or other bindings) when the linker is disabled.
Normally the linker would remove the 32bits parts of the bindings
on a 64bits slice (and that would not be noticed). However we can
not assume this will be done for all binding projects, hence this
workaround.
Sebastien Pouliot
Rolf Bjarne Kvinge