Allow Ch18 DPC++ book code samples to compile (#1467)

* Uncommented CMakeLists.txt for Ch18 DPC++ book code samples

* Updated CMakeLists.txt

Author: jimmytwei

Publications/DPC++/Ch18_using_libs/CMakeLists.txt

@@ -1,35 +1,35 @@
 # Copyright (C) 2020 Intel Corporation
 
 # SPDX-License-Identifier: MIT
-# cmake_minimum_required(VERSION 3.4 )
-# project(Chap18 CXX)
-# add_book_sample(
-#     TEST
-#     TARGET fig_18_1_builtin
-#     SOURCES fig_18_1_builtin.cpp)
+cmake_minimum_required(VERSION 3.4 )
+project(Chap18 CXX)
+add_book_sample(
+    TEST
+    TARGET fig_18_1_builtin
+    SOURCES fig_18_1_builtin.cpp)
 
-# add_book_sample(
-#     TEST
-#     TARGET fig_18_7_swap
-#     SOURCES fig_18_7_swap.cpp)
+add_book_sample(
+    TEST
+    TARGET fig_18_7_swap
+    SOURCES fig_18_7_swap.cpp)
 
-# if(NOT NODPL)
-# add_book_sample(
-#     TEST
-#     TARGET fig_18_11_std_fill
-#     SOURCES fig_18_11_std_fill.cpp)
-# endif()
+if(NOT NODPL)
+add_book_sample(
+    TEST
+    TARGET fig_18_11_std_fill
+    SOURCES fig_18_11_std_fill.cpp)
+endif()
 
-# if(NOT NODPL)
-# add_book_sample(
-#     TEST
-#     TARGET fig_18_13_binary_search
-#     SOURCES fig_18_13_binary_search.cpp)
-# endif()
+if(NOT NODPL)
+add_book_sample(
+    TEST
+    TARGET fig_18_13_binary_search
+    SOURCES fig_18_13_binary_search.cpp)
+endif()
 
-# if(NOT NODPL)
-# add_book_sample(
-#     TEST
-#     TARGET fig_18_15_pstl_usm
-#     SOURCES fig_18_15_pstl_usm.cpp)
-# endif()
+if(NOT NODPL)
+add_book_sample(
+    TEST
+    TARGET fig_18_15_pstl_usm
+    SOURCES fig_18_15_pstl_usm.cpp)
+endif()