[llvm-nm] Report '.comment' ELF sections as 'n' instead of '?'
The previous implementation reported .comment sections as '?'
GNU uses 'n' which means "The symbol is a debugging symbol." .note sections are represented as 'n' too.
The test related to this change was updated to CHECK-NEXT to ensure
order and that we did not miss any symbols in the dump.
Reviewed By: jhenderson
Subscribers: rupprecht, llvm-commits
Differential Revision: https://reviews.llvm.org/D57544