Reproduction Steps:
1. Open User's project
2. Set Scripting Backend to IL2CPP
3. Open "ffi_unity.cs" and "ffi.cs"
Correct:
4. Set print_and_change_value_ios parameter to "ref"
5. Build for iOS
6. In Xcode console notice that "argument current value is 11" is printed
Incorrect:
7. Change print_and_change_value_ios parameter to "out"
8. Build for iOS
9. Notice that "argument current value is 0" is printed.

Note: User included very useful README.md that explains the bug more in depth.

Expected behaviour: Ref and Out keywords work the same.
Actual result: C# Out keyword is working incorrectly with IL2CPP code generation.

Reproduced on versions: Unity 5.5.6f1, 5.6.5p1, 2017.1.3p1, 2017.2.1p3, 2017.3.1f1, 2018.1.0b6
Reproduced on device: iPhone 7 Plus iOS 10.3.2
Did not reproduce with Mono.