Verifying Xcode is installed on High-Sierra
The screenshot you provided tests only the installation of Command Line Tools which sit in /Library/Developer/CommandLineTools. However some software can require full Xcode app to work/install properly. 

xcode-select -p Shows where the complier looks for packages. If this shows /Library/Developer/CommandLineTools and the software installs properly, you don't need full app. But if the software needs it, you need to install Xcode App from the App Store or the website and update the path using 



sudo xcode-select -r


which resets it, or 

sudo xcode-select -switch /Applications/Xcode.app/Contents/Developer


with appropriate path to Xcode.app.

Your test: /usr/bin/xcodebuild -version highlights this issue. On my Mac, with Xcode app, it shows 

Xcode 10.3
Build version 10G8


So follow the instructions here


Download older version of Xcode?


to get the Xcode app, move it to appropriate place, run the path switching command with correct path to Xcode. And proceed with the installation.  

@jmh: "X-code V 10.1 is the latest version of X-Code for High Sierra."

OP: "Link to Xcode 10.1"