[Bug] unity ios crash log can't restore li2cpp stack symbol but the third party Library is fine

### [REQUIRED] Please fill in the following fields:

* Unity editor version: 2018.4.23f1
* Firebase Unity SDK version: 8.6.2
* Source you installed the SDK: .unitypackage
* Problematic Firebase Component: Crashlytics
* Other Firebase Components in use: Google Analytics
* Additional SDKs you are using: none
* Platform you are using the Unity editor on: mac
* Platform you are targeting: iOS
* Scripting Runtime: IL2CPP

### [REQUIRED] Please describe the issue here:


#### Steps to reproduce:

1、Create empty unity project
2、Set up filebase sdk width Crashlytics and Analytics
3、Write some crash code and trigger with button click event.
4、Build the project with ios and install on the iphone
5、Open The Xcode Project And Run Product->Archive
6、Open the Xcode Organizer window and Find the dSYM file in .xcarchive
7、Upload dSYM file width command "/path/to/pods/directory/FirebaseCrashlytics/upload-symbols -gsp /path/to/GoogleService-Info.plist -p ios /path/to/dSYMs"
8、Click the button and the app will crash
9、See the creash report on firebse crashlytics

#### Relevant Code
[Code.zip](https://github.com/firebase/quickstart-unity/files/7659791/Code.zip)