fix hoist_props on const (#2724)

fixes #2710

lib/compress.js

@@ -3274,6 +3274,7 @@ merge(Compressor.prototype, {
                     && (def = sym.definition()).escaped != 1
                     && !def.single_use
                     && !def.direct_access
+                    && !compressor.exposed(def)
                     && !top_retain(def)
                     && (value = sym.fixed_value()) === node.value
                     && value instanceof AST_Object) {

test/compress/hoist_props.js

@@ -827,3 +827,73 @@ issue_2519: {
     }
     expect_stdout: "5.5"
 }
+
+toplevel_const: {
+    options = {
+        hoist_props: true,
+        reduce_vars: true,
+        toplevel: false,
+    }
+    input: {
+        const a = {
+            b: 1,
+            c: 2
+        };
+        console.log(a.b + a.c);
+    }
+    expect: {
+        const a = {
+            b: 1,
+            c: 2
+        };
+        console.log(a.b + a.c);
+    }
+    expect_stdout: "3"
+}
+
+toplevel_let: {
+    options = {
+        hoist_props: true,
+        reduce_vars: true,
+        toplevel: false,
+    }
+    input: {
+        let a = {
+            b: 1,
+            c: 2
+        };
+        console.log(a.b + a.c);
+    }
+    expect: {
+        let a = {
+            b: 1,
+            c: 2
+        };
+        console.log(a.b + a.c);
+    }
+    expect_stdout: "3"
+    node_version: ">=6"
+}
+
+toplevel_var: {
+    options = {
+        hoist_props: true,
+        reduce_vars: true,
+        toplevel: false,
+    }
+    input: {
+        var a = {
+            b: 1,
+            c: 2
+        };
+        console.log(a.b + a.c);
+    }
+    expect: {
+        var a = {
+            b: 1,
+            c: 2
+        };
+        console.log(a.b + a.c);
+    }
+    expect_stdout: "3"
+}