Added "used" attribute to entries in yosys_cover_list
Added "used" attribute to entries in yosys_cover_list

http://www.reddit.com/r/yosys/comments/2kw479/fyi_clang_350_build_error/cltgwyc
http://llvm.org/bugs/show_bug.cgi?id=19474

YosysHQ/yosys,antmicro/yosys,SymbiFlow/yosys,azonenberg/yosys,YosysHQ/yosys,YosysHQ/yosys,azonenberg/yosys,azonenberg/yosys,swallat/yosys,antmicro/yosys,antmicro/yosys,azonenberg/yosys,swallat/yosys,azonenberg/yosys,SymbiFlow/yosys,SymbiFlow/yosys,cliffordwolf/yosys,cliffordwolf/yosys,SymbiFlow/yosys,SymbiFlow/yosys,cliffordwolf/yosys,cliffordwolf/yosys,swallat/yosys,azonenberg/yosys,azonenberg/yosys,swallat/yosys,cliffordwolf/yosys,antmicro/yosys,cliffordwolf/yosys,YosysHQ/yosys,swallat/yosys,antmicro/yosys,antmicro/yosys,SymbiFlow/yosys,azonenberg/yosys,YosysHQ/yosys,swallat/yosys,YosysHQ/yosys,YosysHQ/yosys,antmicro/yosys,cliffordwolf/yosys,cliffordwolf/yosys,antmicro/yosys,swallat/yosys,SymbiFlow/yosys,SymbiFlow/yosys,YosysHQ/yosys,cliffordwolf/yosys,swallat/yosys,azonenberg/yosys,swallat/yosys