Reproduction Steps:
1. Build project for iOS (building steps in edit)
2. In Xcode build (profile) and launch Instruments
3. Instruments select "Time Profiler"
4. Record/Profile
5. Select first 10 seconds
6. Notice that MonoManager::GetScriptingClass takes a lot of time

Expected behaviour: Optimal Unity application loading
Actual result: Loading Unity application string allocations/deallocations/comparisons takes a lot of time.

Reproduced on versions: Unity 2017.3.0f3, 2017.3.0p3
Project crashed on opening with Unity 2018
Reproduced on devices: iPhone 7 Plus iOS 10.3.2, iPhone 5 iOS 10.1.1, iPhone 4s iOS 8.2