Fix back wrong C_FLAGS for vlsift.
Fix back wrong C_FLAGS for vlsift.

poparteu/openMVG,openMVG/openMVG,poparteu/openMVG,openMVG/openMVG,openMVG/openMVG,openMVG/openMVG,poparteu/openMVG,poparteu/openMVG,openMVG/openMVG