glx: try swrastg_dri, if swrast_dri fails
glx: try swrastg_dri, if swrast_dri fails

This needs a patch for xserver/glx also. An enviroment variable will be added
at some point, it chould be for swrastg only or all gallium drivers.

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