[MCJIT] Add a 'decodeAddend' method to RuntimeDyldMachO and teach
getBasicRelocationEntry to use this rather than 'memcpy' to get the
relocation addend. Targets with non-trivial addend encodings (E.g. AArch64) can
override decodeAddend to handle immediates with interesting encodings.

No functional change.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213435 91177308-0d34-0410-b5e6-96231b3b80d8