[ELF] - do not create special symbols when creating relocatable output

__start_/__end_ <section-name> symbols and other specials like:
preinit_array_start/end
init_array_start/end
fini_array_start/end

should not be created by linker when creating relocatable files.

Differential revision: http://reviews.llvm.org/D17774

llvm-svn: 262366