rustc: Fix bug involving extracting any variant element beyond the first. Un-XFAIL alt-tag.rs.

src/Makefile

@@ -519,6 +519,7 @@ TEST_XFAILS_LLVM := $(TASK_XFAILS) \
 
 TEST_XFAILS_SELF := $(filter-out \
                       $(addprefix test/run-pass/, \
+                        alt-tag.rs \
                         arith-0.rs \
                         arith-1.rs \
                         arith-2.rs \

src/comp/middle/trans.rs

@@ -1425,6 +1425,7 @@ fn get_pat_union_ptr(@block_ctxt cx, vec[@ast.pat] subpats, ValueRef llval)
                 auto subpat_res = trans_pat_binding(this_cx, subpat,
                                                     llsubval);
                 this_cx = subpat_res.bcx;
+                i += 1;
             }
 
             ret res(this_cx, llval);