[JITLink][ELF] Support duplicated section names from object file

ELF object files can contain duplicated sections (thus section symbols
as well), espeically when comdats/section groups are present. This patch
adds support for generating LinkGraph from object files that have
duplicated section names. This is the first step to properly model
comdats/section groups.

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D114753