package/glmark2: needs gcc >= 4.9 for C++14

Fixes:
    http://autobuild.buildroot.org/results/511/51162285d197deabb63727c19cdf5512b0e68f29/



[Peter: also add libstdcpp dependency]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Bernd Kuhls <bernd.kuhls@t-online.de>
Cc: Spenser Gilliland <spenser@gillilanding.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>