Fix the build with clang 6.
There's no point in making old, unmaintained code be C++11 compliant, so just
build with -std=gnu++98.
qvideosurfacegstsink.cpp:345:73: error: constant expression evaluates to 4278190080 which cannot be narrowed to type 'int' [-Wc++11-narrowing]
{ QVideoFrame::Format_RGB32 , 32, 24, 4321, 0x0000FF00, 0x00FF0000, 0xFF000000, 0x00000000 },
^~~~~~~~~~(and others)