softpipe: set dirty_render_cache in softpipe_clear()
softpipe: set dirty_render_cache in softpipe_clear()

This fixes a bug seen when doing a glDrawPixels(GL_STENCIL_INDEX) right
after a glClear().  The check-for-flush test was failing because we
didn't set the dirty_render_cache flag in softpipe_clear().  So we saw
stale data when we mapped the stencil buffer.

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