CMake: Use the GNUInstallDirs module

CMakeLists.txt

@@ -1,5 +1,7 @@
 cmake_minimum_required(VERSION 2.8)
 
+include(GNUInstallDirs)
+
 project(cJSON C)
 
 set(CJSON_VERSION_MAJOR 1)
@@ -15,7 +17,7 @@ endif()
 
 #variables for pkg-config
 set(prefix "${CMAKE_INSTALL_PREFIX}")
-set(libdir "${CMAKE_INSTALL_PREFIX}/lib")
+set(libdir "${CMAKE_INSTALL_FULL_LIBDIR}")
 set(version "${CJSON_VERSION}")
 
 option(BUILD_SHARED_LIBS "Build shared libraries" ON)
@@ -34,9 +36,9 @@ endif()
 configure_file("${CMAKE_CURRENT_SOURCE_DIR}/libcjson.pc.in"
     "${CMAKE_CURRENT_BINARY_DIR}/libcjson.pc" @ONLY)
 
-install(TARGETS "${CJSON_LIB}" DESTINATION "lib${LIB_SUFFIX}")
-install(FILES cJSON.h DESTINATION include/cjson)
-install (FILES "${CMAKE_CURRENT_BINARY_DIR}/libcjson.pc" DESTINATION lib/pkgconfig)
+install(TARGETS "${CJSON_LIB}" DESTINATION "${CMAKE_INSTALL_LIBDIR}")
+install(FILES cJSON.h DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/cjson")
+install (FILES "${CMAKE_CURRENT_BINARY_DIR}/libcjson.pc" DESTINATION "${CMAKE_INSTALL_LIBDIR}/pkgconfig")
 
 set_target_properties("${CJSON_LIB}"
     PROPERTIES
@@ -57,9 +59,9 @@ if(ENABLE_CJSON_UTILS)
     configure_file("${CMAKE_CURRENT_SOURCE_DIR}/libcjson_utils.pc.in"
         "${CMAKE_CURRENT_BINARY_DIR}/libcjson_utils.pc" @ONLY)
 
-    install(TARGETS "${CJSON_UTILS_LIB}" DESTINATION "lib${LIB_SUFFIX}")
-    install(FILES cJSON_Utils.h DESTINATION include/cjson)
-    install (FILES "${CMAKE_CURRENT_BINARY_DIR}/libcjson_utils.pc" DESTINATION lib/pkgconfig)
+    install(TARGETS "${CJSON_UTILS_LIB}" DESTINATION "${CMAKE_INSTALL_LIBDIR}")
+    install(FILES cJSON_Utils.h DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/cjson")
+    install (FILES "${CMAKE_CURRENT_BINARY_DIR}/libcjson_utils.pc" DESTINATION "${CMAKE_INSTALL_LIBDIR}/pkgconfig")
 
     set_target_properties("${CJSON_UTILS_LIB}"
         PROPERTIES