Suppress popup dialog about missing Xcode at configure time

On macOS I get an annoying dialog when running configure on a machine that doesn't have Xcode installed (e.g. because it is new or it has all tools in /nix/store).

I think that configure shouldn't bring up any dialog. The new test consults xcode-select first, asking for the installation path, and only if that succeeds, it proceeds with querying xcodebuild. Both tools are present on a pristine system (actually xcodebuild bounces to xcode-select).

Now I get in the ./configure output

checking XCode version... not found (too old?)

on such an Xcode-less system, whereas previously there would be a mixed (with stderr) output like below

checking XCode version... xcode-select: note: no developer tools were found at '/Applications/Xcode.app', requesting install. Choose an option in the dialog to download the command line developer tools.
not found (too old?)

Note: I am looking for testers who have Xcode installed.