This adds -z muldefs option which is widely used over --allow-multiple-definition. This option is supported by the GNU linker. llvm-svn: 205391
If --allow-multiple-definition option is given, LLD does not treat duplicate symbol error as a fatal error. GNU LD supports this option. Differential Revision: http://llvm-reviews.chandlerc.com/D3211 llvm-svn: 205015