[iOS] make AOT code PIC compatible
Workaround for case 539074
(crash while handling exception in external assembly after script reload in play mode)
Fixed upstream in a4bac650
Update classlibs build script.
Remove superfluous build failures.
Set PATH on build agents.
Merge pull request #68 from Unity-Technologies/ios/make-AOT-PIE

[iOS] make AOT code PIC compatible
Merge pull request #69 from Unity-Technologies/unity-staging

PIC on iOS and build script changes