fork of dune legacy from sourceforge: https://sourceforge.net/p/dunelegacy/code/
Jump over to Releases and download/install the Dune Legacy.dmg release, it might even work..!
This is tested with XCode 8.1 on Sierra.
git clone https://github.com/philippkeller/dunelegacy.git
cd dunelegacy/IDE/xCode
mkdir -p ~/Library/Frameworks/
open Dune\ Legacy.xcodeproj
Building (Shift-⌘-R) should work out of the box, the application is put into ~/Library/Developer/Xcode/DerivedData/Dune_Legacy-..../Build/Products/Debug/Dune Legacy.app, the exact path you see in the right column when you click on "Dune Legacy.app" bottom left
You can also clone from the original git repo. Chances are that I cannot keep up with this repo -> you're better served by cloning from the [original sourceforge repo](git://git.code.sf.net/p/dunelegacy/code dunelegacy-code). The howto above should work as well.