[ELF] Return the section name when calling getSymbolName on a section symbol.

Summary:
Previously, llvm-nm would report symbols for .debug and .note sections as: '?' with an empty  section name:

```
00000000 ?
00000000 ?
...
```

With this patch the output more closely resembles GNU nm:
```
00000000 N .debug_abbrev
00000000 n .note.GNU-stack
...
```

This patch calls `getSectionName` for sections that belong to symbols of type `ELF::STT_SECTION`, which returns the name of the section from the section string table.

Reviewers: Bigcheese, davide, jhenderson

Reviewed By: davide, jhenderson

Subscribers: rupprecht, jhenderson, llvm-commits

Differential Revision: https://reviews.llvm.org/D57105

llvm-svn: 352785
3 files changed
tree: e503623a41161f8bf1c97768d3d21c0ac2ea36b7
  1. clang/
  2. clang-tools-extra/
  3. compiler-rt/
  4. debuginfo-tests/
  5. libclc/
  6. libcxx/
  7. libcxxabi/
  8. libunwind/
  9. lld/
  10. lldb/
  11. llgo/
  12. llvm/
  13. openmp/
  14. parallel-libs/
  15. polly/
  16. pstl/
  17. .arcconfig
  18. .clang-format
  19. .clang-tidy
  20. README.md
README.md

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