[ELF2] - Basic implementation of -r/--relocatable

Description

[ELF2] - Basic implementation of -r/--relocatable

-r, -relocatable - Generate relocatable output

Currently does not have support for files containing
relocation sections with entries that refer to local
symbols (like rel[a].eh_frame which refer to sections
and not to symbols)

Differential revision: http://reviews.llvm.org/D14382

Details