Implement getRelocationAddress for MachO and ET_REL elf files.

With that, fix the symbolizer to work with any ELF file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205588 91177308-0d34-0410-b5e6-96231b3b80d8
Add an assert that this is only used with .o files.

I am not sure how to get a relocation in a .dylib, but this function would
return the wrong value if passed one.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205592 91177308-0d34-0410-b5e6-96231b3b80d8