Set the new vec fill-size on the compiler side, as in rustboot. Un-XFAIL first 3 vec tests.

src/Makefile

@@ -558,6 +558,9 @@ TEST_XFAILS_SELF := $(filter-out \
                         u8-incr-decr.rs \
                         uint.rs \
                         unit.rs \
+                        vec.rs \
+                        vec-in-tup.rs \
+                        vec-late-init.rs \
                         while-and-do-while.rs \
                         writealias.rs \
                         ) \

src/comp/middle/trans.rs

@@ -1376,6 +1376,7 @@ fn trans_index(@block_ctxt cx, &ast.span sp, @ast.expr base,
 
     auto lim = ix.bcx.build.GEP(v, vec(C_int(0), C_int(abi.vec_elt_fill)));
     lim = ix.bcx.build.Load(lim);
+
     auto bounds_check = ix.bcx.build.ICmp(lib.llvm.LLVMIntULT,
                                           scaled_ix, lim);
 
@@ -1582,6 +1583,10 @@ impure fn trans_vec(@block_ctxt cx, vec[@ast.expr] args,
         sub = copy_ty(src_res.bcx, true, dst_elt, src_res.val, unit_ty);
         i += 1;
     }
+    auto fill = sub.bcx.build.GEP(vec_val,
+                                  vec(C_int(0), C_int(abi.vec_elt_fill)));
+    sub.bcx.build.Store(data_sz, fill);
+
     ret res(sub.bcx, vec_val);
 }