Cleanup relocation sorting for ELF.

We want the order to be deterministic on all platforms. NAKAMURA Takumi
fixed that in r181864. This patch is just two small cleanups:

* Move the function to the cpp file. It is only passed to array_pod_sort.
* Remove the ppc implementation which is now redundant

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181910 91177308-0d34-0410-b5e6-96231b3b80d8