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