[llvm-objdump] Should print strings when dumping DT_RPATH, DT_RUNPATH,...

[llvm-objdump] Should print strings when dumping DT_RPATH, DT_RUNPATH, DT_SONAME, DT_AUXILIARY and DT_FILTER tags in dynamic section.

Summary:
Before:
```
Dynamic Section:
  NEEDED               libpthread.so.0
  ...
  NEEDED               ld-linux-x86-64.so.2
  RPATH                0x00000000001c2e61
```

After:
```
Dynamic Section:
  NEEDED               libpthread.so.0
  ...
  NEEDED               ld-linux-x86-64.so.2
  RPATH                $ORIGIN/../lib
```

Only a small problem here, I have no idea on choosing test case. I see there's a test 
file(test/tools/llvm-objdump/private-headers-dynamic-section.test). But it has no DT_RPATH and DT_RUNPATH tags. Shall I replace the ELF file in the 
Inputs dir by a new one?

Reviewers: jhenderson, grimar

Reviewed By: jhenderson

Subscribers: srhines, rupprecht, jfb, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58707

llvm-svn: 355001