Upgrading OSX/Xcode - linking failure
Solving in somewhat unusual way:

a) You claim "However linking succeeded.", so in project properties pane, go to Products folder, then click on product name. On the right-side pane, under Identity and Type, you will find out the name of the product and the full path location. For one of my projects now i can find out: 


  ~/Library/Developer/Xcode/DerivedData/prodname fnihcmsxnrxlstcumyviklyuofum/Build/Products/Debug/prodname


and a location attribute: Relative to Build Products - build folder was create by Xcode, you can find out "Build" also in Project Properties -> Build Settings -> Build Locations. (you can modify also according to your needs...)

b) Now for your missing library: also in Build Settings -> Linking you have the possibility to add your library at Prelink libraries, just click at the left of this item, two lines open below, Debug/Release, click on one line and a small + appears and add your library there.

EDIT: adding some pictures, as requested:

Selecting the Product:



Click on product name (rectangle on the picture) and the full path is to be found  on the right pane as in this picture:



Now, in the first picture: click on application name icon, will open building info. Building path(s) are to be found as shown here:



And scrolling down further, the linking options as revealed here: