I was able run the app in the simulator however running it one of the devices ran into the error
dyld: Library not loaded: @rpath/libswiftCore.dylib Referenced from: /var/mobile/Containers/Bundle/Application/3FC2DC5C-A908-42C4-8508-1320E01E0D5B/Stylist.app/Stylist Reason: no suitable image found. Did find: /private/var/mobile/Containers/Bundle/Application/3FC2DC5C-A908-42C4-8508-1320E01E0D5B/testapp.app/Frameworks/libswiftCore.dylib: mmap() errno=1 validating first page of '/private/var/mobile/Containers/Bundle/Application/3FC2DC5C-A908-42C4-8508-1320E01E0D5B/testapp.app/Frameworks/libswiftCore.dylib' (lldb)
It turns out that Xcode cache some device specific stuff which can get mixed up if you are running your apps on multiple devices. The simple fix is to delete Xcode cache. The following command clean it up for you
rm -rf "$(getconf DARWIN_USER_CACHE_DIR)/org.llvm.clang/ModuleCache" rm -rf ~/Library/Developer/Xcode/DerivedData rm -rf ~/Library/Caches/com.apple.dt.Xcode