Fail if the CLI SAPI is not used to invoke composer

bin/composer

@@ -1,6 +1,11 @@
 #!/usr/bin/env php
 <?php
 
+if (PHP_SAPI !== 'cli') {
+    echo 'Composer should be invoked via the CLI version of PHP, not the '.PHP_SAPI.' SAPI'.PHP_EOL;
+    exit(1);
+}
+
 require __DIR__.'/../src/bootstrap.php';
 
 use Composer\Console\Application;