progs/trivial: use -c option to use glCopyPixels()
progs/trivial: use -c option to use glCopyPixels()

Otherwise we use glRead/DrawPixels to copy the off-screen FBO image
into the window.

Looks like NVIDIA's broken when using -c (the image is upside down),
but OK with -c -t.

jbarczak/glsl-optimizer,benaadams/glsl-optimizer,djreep81/glsl-optimizer,wolf96/glsl-optimizer,djreep81/glsl-optimizer,mcanthony/glsl-optimizer,zeux/glsl-optimizer,djreep81/glsl-optimizer,KTXSoftware/glsl2agal,bkaradzic/glsl-optimizer,djreep81/glsl-optimizer,adobe/glsl2agal,tokyovigilante/glsl-optimizer,zz85/glsl-optimizer,KTXSoftware/glsl2agal,dellis1972/glsl-optimizer,benaadams/glsl-optimizer,dellis1972/glsl-optimizer,zeux/glsl-optimizer,zz85/glsl-optimizer,adobe/glsl2agal,mcanthony/glsl-optimizer,bkaradzic/glsl-optimizer,adobe/glsl2agal,metora/MesaGLSLCompiler,KTXSoftware/glsl2agal,zeux/glsl-optimizer,zz85/glsl-optimizer,zeux/glsl-optimizer,wolf96/glsl-optimizer,KTXSoftware/glsl2agal,benaadams/glsl-optimizer,jbarczak/glsl-optimizer,benaadams/glsl-optimizer,tokyovigilante/glsl-optimizer,wolf96/glsl-optimizer,bkaradzic/glsl-optimizer,zz85/glsl-optimizer,dellis1972/glsl-optimizer,zeux/glsl-optimizer,zz85/glsl-optimizer,jbarczak/glsl-optimizer,mapbox/glsl-optimizer,bkaradzic/glsl-optimizer,tokyovigilante/glsl-optimizer,metora/MesaGLSLCompiler,adobe/glsl2agal,wolf96/glsl-optimizer,mcanthony/glsl-optimizer,mapbox/glsl-optimizer,mcanthony/glsl-optimizer,tokyovigilante/glsl-optimizer,mapbox/glsl-optimizer,mapbox/glsl-optimizer,djreep81/glsl-optimizer,dellis1972/glsl-optimizer,benaadams/glsl-optimizer,bkaradzic/glsl-optimizer,jbarczak/glsl-optimizer,mapbox/glsl-optimizer,mcanthony/glsl-optimizer,jbarczak/glsl-optimizer,adobe/glsl2agal,zz85/glsl-optimizer,KTXSoftware/glsl2agal,dellis1972/glsl-optimizer,benaadams/glsl-optimizer,wolf96/glsl-optimizer,metora/MesaGLSLCompiler,tokyovigilante/glsl-optimizer