fix corner case in hoist_props (#4986)

fixes #4985

lib/compress.js

@@ -7432,7 +7432,8 @@ merge(Compressor.prototype, {
                 && all(right.properties, can_hoist_property)
                 && all(def.references, function(ref) {
                     return ref.fixed_value() === right;
-                });
+                })
+                && can_drop_symbol(sym, compressor);
         }
     });
 

test/compress/let.js

@@ -1580,3 +1580,27 @@ issue_4848: {
     expect_stdout: "PASS"
     node_version: ">=4"
 }
+
+issue_4985: {
+    options = {
+        hoist_props: true,
+        reduce_vars: true,
+        toplevel: true,
+    }
+    input: {
+        "use strict";
+        let a = { p: 42 };
+        console.log(function() {
+            a;
+        }());
+    }
+    expect: {
+        "use strict";
+        let a = { p: 42 };
+        console.log(function() {
+            a;
+        }());
+    }
+    expect_stdout: "undefined"
+    node_version: ">=4"
+}