glsl: Vectorize multiple scalar assignments

Reduces vertex shader instruction counts in DOTA2 by 6.42%, L4D2 by
4.61%, and CS:GO by 5.71%.

total instructions in shared programs: 1500153 -> 1498191 (-0.13%)
instructions in affected programs:     59919 -> 57957 (-3.27%)

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/glsl/glsl_parser_extras.cpp

@@ -1564,6 +1564,10 @@ do_common_optimization(exec_list *ir, bool linked,
    if (options->OptimizeForAOS && !linked)
       progress = opt_flip_matrices(ir) || progress;
 
+   if (linked && options->OptimizeForAOS) {
+      progress = do_vectorize(ir) || progress;
+   }
+
    if (linked)
       progress = do_dead_code(ir, uniform_locations_assigned) || progress;
    else