[MCJIT] Fix the alignment requirements for ARM and AArch64 which were mistakenly

relaxed in the big RuntimeDyldMachO cleanup of r213293.

No test case yet - this was found via inspection and there's no easy way to test
GOT alignment in RuntimeDyldChecker at the moment. I'm working on adding support
for this now, and hope to have a test case for this soon.

llvm-svn: 213331