Fix MachO arm64 delta32ToGOT reloc encoding in -r.

The fixup content we encode here should be the offset from the
fixup location back to the last nonlocal label.  We were only encoding
the address of the fixup, and not taking in to account the base address
of the atom we are in.

Updated the test case here to have a text section which will come before
the data section where the relocation lives.  .data being at offset 0 had
previously been hiding this bug.

llvm-svn: 256974