Handle relocations that don't point to symbols.

In ELF (as in MachO), not all relocations point to symbols. Represent this
properly by using a symbol_iterator instead of a SymbolRef. Update llvm-readobj
ELF's dumper to handle relocatios without symbols.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183284 91177308-0d34-0410-b5e6-96231b3b80d8
Revert "R600: Add a pass that merge Vector Register"

This reverts commit r183279. CodeGen/R600/texture-input-merge.ll was failing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183286 91177308-0d34-0410-b5e6-96231b3b80d8