aux/draw: use nir_to_tgsi for draw shader in llvm path
Older vmware's SVGA device doesn't support PIPE_CAP_LOAD_CONSTBUF. This leads to using load_ubo_vec4 which throws llvmpipe off the guard since it doesn't expect load_ubo_vec4 in shader. Use nir_to_tgsi utility in such a case.
This fixes crash seen with conform's mustpass.c, select.c and feedback.c. Also, few gl-select related piglit tests exhibit same crash
Reviewed-by: Charmaine Lee firstname.lastname@example.org