Pass small fixed-size arrays as immediates

Currently even small fixed-size arrays are passed as indirect
parameters, which seems to be just an oversight. Let's handle them the
same as structs of the same size, passing them as immediate values.

Author: dotdash

src/librustc_trans/trans/common.rs

@@ -244,7 +244,7 @@ pub fn type_is_immediate<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, ty: Ty<'tcx>) -
         return false;
     }
     match ty.sty {
-        ty::ty_struct(..) | ty::ty_enum(..) | ty::ty_tup(..) |
+        ty::ty_struct(..) | ty::ty_enum(..) | ty::ty_tup(..) | ty::ty_vec(_, Some(_)) |
         ty::ty_unboxed_closure(..) => {
             let llty = sizing_type_of(ccx, ty);
             llsize_of_alloc(ccx, llty) <= llsize_of_alloc(ccx, ccx.int_type())