update Makefile to support C++11 and g++-4.8
update Makefile to support C++11 and g++-4.8

ydwu/gunrock,ydwu/gunrock,ydwu/gunrock,Damien-/gunrock,Damien-/gunrock,anshumang/gunrock-swched-swmm,Damien-/gunrock,ydwu/gunrock,ydwu/gunrock,anshumang/gunrock-swched-swmm,Damien-/gunrock,Damien-/gunrock,anshumang/gunrock-swched-swmm,anshumang/gunrock-swched-swmm,anshumang/gunrock-swched-swmm