set verbosity following system.debug variable. See https://www.visualstudio.com/en-us/docs/build/define/variables

Author: tomap

src/GitVersionTfsTask/GitVersion.ps1

@@ -54,6 +54,13 @@ if($additionalArguments)
   $argsGitVersion = $argsGitVersion + " $additionalArguments"
 }
 
+if(!$additionalArguments -or !$additionalArguments.Contains("-debug"))
+{
+  if([string]::IsNullOrEmpty($env:SYSTEM_DEBUG) -or $env:SYSTEM_DEBUG -ne "true"){
+    $argsGitVersion = $argsGitVersion + " -verbosity Error"
+  }
+}
+
 Write-Host (Get-LocalizedString -Key "Invoking GitVersion with {0}" -ArgumentList $argsGitVersion)
 
 Invoke-Tool -Path $GitVersionPath -Arguments "$argsGitVersion"