Issue with marshaling of delegates as fields of a struct when using IL2CPP - As noted by the user, there are no issues when using the Mono backend.

Originally reported at: https://community.unity.com/t5/Scripting/IL2CPP-MarshalDirectiveException/m-p/2648350#U2648350

Bug reported at the request of Joshua Peterson.

Steps to Reproduce
------------------------
1.Download the users reproduction project ('New Unity Project.zip').
2.Open in the editor and switch to a platform that supports IL2CPP.
3.Check that the scripting back-end is set to IL2CPP
4.Important: Tick 'Development Build' in the player settings (otherwise you won't see the exception in the TTY)
4.Select Build and Run

Result:
Running a build produced with '5.4.0f1' the following exception is spammed to the TTY:

--
Initializing client
UnityEngine.DebugLogHandler:Internal_Log(LogType, String, Object)
UnityEngine.DebugLogHandler:LogFormat(LogType, Object, String, Object[])
UnityEngine.Logger:Log(LogType, Object)
UnityEngine.Debug:Log(Object)
SAMTest:Update()

(Filename: C:/buildslave/unity/build/artifacts/generated/common/runtime/UnityEngineDebugBindings.gen.cpp Line: 42)

MarshalDirectiveException: Cannot marshal field 'gameWorldReservedCB' of type 'SAMCallbacks': Reference type field marshalin
g is not supported.
at SAMTest.samInitialize (IntPtr inParams, SAMCallbacks& callbacks) [0x00000] in <filename unknown>:0
at SAMTest.Update () [0x00000] in <filename unknown>:0

(Filename: currently not available on il2cpp Line: -1)
--

Reproduced in:
5.4.0f1 (c6df7519ab13)
5.3.5p8 (4ff20829e874)
5.3.5p4 (f55402cb6571)