Add gui-private include dirs for Qt5 (#768)

Author: n-elie

src/CMakeLists.txt

@@ -13,8 +13,8 @@ if (UNIX AND NOT APPLE AND QT_VERSION_MAJOR STREQUAL "6" AND QT_VERSION_MINOR GR
     set(ads_DEP_LIBS Core Gui GuiPrivate Widgets)
 endif()
 find_package(Qt${QT_VERSION_MAJOR} COMPONENTS ${ads_DEP_LIBS} REQUIRED)
-if (UNIX AND NOT APPLE AND QT_VERSION_MAJOR STREQUAL "6" AND QT_VERSION_MINOR GREATER 8)
-    include_directories(${Qt${QT_VERSION_MAJOR}Gui_PRIVATE_INCLUDE_DIRS})
+if (UNIX AND NOT APPLE AND ((QT_VERSION_MAJOR STREQUAL "6" AND QT_VERSION_MINOR GREATER 8) OR QT_VERSION_MAJOR STREQUAL "5"))
+     include_directories(${Qt${QT_VERSION_MAJOR}Gui_PRIVATE_INCLUDE_DIRS})
 endif()
 
 set(CMAKE_INCLUDE_CURRENT_DIR ON)