ELFRelocationEntry::operator<(): Try to stabilize the order. r_offset was insufficient to sort Relocs.

It should fix llvm/test/CodeGen/ARM/ehabi-mc-compact-pr*.ll on some hosts.

  RELOCATION RECORDS FOR [.ARM.exidx]:
  0 R_ARM_PREL31 .text
  0 R_ARM_NONE __aeabi_unwind_cpp_pr0

FIXME: I am not sure of the directions of extra comparators, in Type and Index.
For now, they are different from the direction in r_offset.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181864 91177308-0d34-0410-b5e6-96231b3b80d8