mesa: Make _mesa_GetActiveAttribARB use the attributes in the shader IR

mesa: Make _mesa_GetActiveAttribARB use the attributes in the shader IR

Instead of relying on the mirror in the Mesa IR assembly shader, just
use the variables actually stored in the GLSL IR.  This will be a bit
slower, but nobody cares about the performance of glGetActiveAttrib.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>