glx: Store the RENDER_TYPE in indirect rendering

v2 (idr): Open-code the check for GLX_RENDER_TYPE.
dri2_convert_glx_attribs can't be called from here because that function
only exists in direct-rendering builds.  Also add a stub version of
indirect_create_context_attribs to tests/fake_glx_screen.cpp to prevent
'make check' regressions.

Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/glx/glxcmds.c

@@ -344,7 +344,6 @@ CreateContext(Display *dpy, int generic_id, struct glx_config *config,
 
    gc->share_xid = shareList ? shareList->xid : None;
    gc->imported = GL_FALSE;
-   gc->renderType = renderType;
 
    return (GLXContext) gc;
 }