Clean up GCC flags
Clean up GCC flags

Remove some redundant or repeated flags, as noted by ppannuto in Issue #23.

KeelanArrendale/zmap,cicku/zmap,zhuyue1314/zmap,unixfreaxjp/zmap,tdi/zmap,shakenetwork/zmap,BobuSumisu/zmap,unixfreaxjp/zmap,shakenetwork/zmap,cicku/zmap,cicku/zmap,willscott/zmap,scarito/zmap,potatozhao/zmap,KeelanArrendale/zmap,eacha/zmap,scarito/zmap,zhuyue1314/zmap,KeelanArrendale/zmap,scarito/zmap,zmap/zmap,potatozhao/zmap,eacha/zmap,unixfreaxjp/zmap,eacha/zmap,scarito/zmap,BobuSumisu/zmap,shakenetwork/zmap,willscott/zmap,BobuSumisu/zmap,shakenetwork/zmap,coydog/zmap-freebsd,3L3N4/zmap,potatozhao/zmap,3L3N4/zmap,unixfreaxjp/zmap,djeraseit/zmap,potatozhao/zmap,BobuSumisu/zmap,potatozhao/zmap,zmap/zmap,3L3N4/zmap,scarito/zmap-android,zhuyue1314/zmap,willscott/zmap,coolacid/zmap,coolacid/zmap,coydog/zmap-freebsd,djeraseit/zmap,willscott/zmap,djeraseit/zmap,3L3N4/zmap,tdi/zmap,coolacid/zmap,scarito/zmap-android,djeraseit/zmap,tdi/zmap,coolacid/zmap,willscott/zmap,shakenetwork/zmap,scarito/zmap-android,cicku/zmap,KeelanArrendale/zmap,coolacid/zmap,scarito/zmap,tdi/zmap,djeraseit/zmap,tdi/zmap,unixfreaxjp/zmap,eacha/zmap,zhuyue1314/zmap,zhuyue1314/zmap,coydog/zmap-freebsd,scarito/zmap-android,cicku/zmap,zmap/zmap,KeelanArrendale/zmap,eacha/zmap,BobuSumisu/zmap,3L3N4/zmap