xcode not found while building

[Riccardo Mottola]

Hi,

MacVim is difficult to build, I want to get a version build on older 
versions of MacOS.
I am trying to get a version building on 10.11. The current versions and 
most previous versions don't build, because XCode 8 is expected. I have 
XCode 7.3.1

Going back in history I got to 8.1 155

this has build failing.

Hunk #1 succeeded at 796 (offset 27 lines).
--->  Running ibtool for Preferences.nib
xcode-select: error: tool 'ibtool' requires Xcode, but active developer 
directory '/Library/Developer/CommandLineTools' is a command line tools 
instance
Command failed: ibtool --compile 
src/MacVim/English.lproj/Preferences.nib/keyedobjects.nib 
src/MacVim/English.lproj/Preferences.nib
Exit code: 1
Error: Failed to patch MacVim: command execution failed


But, as said, I have XCode installed! what cold be wrong?

Riccardo