Set "use_openssl" gyp variable to 1 if it is undefined

libsrtp.gyp

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'variables': {
     'use_system_libsrtp%': 0,
-    'use_openssl': 1,
+    'use_openssl%': 1,
   },
   'target_defaults': {
     'defines': [
       'HAVE_CONFIG_H',
       'HAVE_STDLIB_H',
       'HAVE_STRING_H',
       'TESTAPP_SOURCE',
     ],
     'include_dirs': [
       './config',
@@ skipping 408 matching lines @@
           'link_settings': {
             'libraries': [
               '-lsrtp',
             ],
           },
         }, # target libsrtp
       ], # targets
     }],
   ],
 }