[MCJIT] Respect target endianness in RuntimeDyldMachO and RuntimeDyldChecker.

This patch may address some of the issues described in http://llvm.org/PR20640.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215938 91177308-0d34-0410-b5e6-96231b3b80d8