Do not restart with cmd.exe if cwd is a UNC path

cmd.exe does not support a UNC path as the working directory and will
change it to the Windows directory before executing any command. We
bypass cmd.exe on PHP 7.4+ by calling the php binary directly so this
only affects earlier versions.

src/XdebugHandler.php

@@ -598,6 +598,15 @@ private function checkConfiguration(&$info)
             }
         }
 
+
+        $workingDir = getcwd();
+        if (0 === strpos($workingDir, '\\\\')) {
+            if (defined('PHP_WINDOWS_VERSION_BUILD') && PHP_VERSION_ID < 70400) {
+                $info = 'cmd.exe does not support UNC paths: '.$workingDir;
+                return false;
+            }
+        }
+
         return true;
     }