[ELF] - Refactoring: reuse similar method.
[ELF] - Refactoring: reuse similar method.

We had assignSymbol and assignSectionSymbol methods which has similar functionality.
Patch removes one of copy and reuses another in code.

Differential revision: https://reviews.llvm.org/D29582

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@294290 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld