Object: Don't double-escape empty hexdata

We would emit a pair of double quotes inside a pair of single quotes.
Just use a pair of single quotes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204312 91177308-0d34-0410-b5e6-96231b3b80d8
Object: Abstract out the determination of function line symbols

No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204313 91177308-0d34-0410-b5e6-96231b3b80d8
Object: Output .file symbols properly

obj2yaml would emit the NUL bytes padding the auxiliary file symbol
records.  Trimming them looks nicer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204314 91177308-0d34-0410-b5e6-96231b3b80d8