[RuntimeDyld] Adds the necessary hooks to MCJIT to be able to debug generated
MachO files using the GDB JIT debugging interface.

Patch by Keno Fischer. Thanks Keno!



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211652 91177308-0d34-0410-b5e6-96231b3b80d8