Check type when struct is matched against enum-like pattern

Previously check always succeeded because struct type was derived from
the matched expression, not the matched pattern.

src/test/compile-fail/match-struct.rs

@@ -0,0 +1,11 @@
+// error-pattern: mismatched types
+
+struct S { a: int }
+enum E { C(int) }
+
+fn main() {
+    match S { a: 1 } {
+        C(_) => (),
+        _ => ()
+    }
+}