Make everything work in cmake 3.8

dlib/test/CMakeLists.txt

@@ -184,7 +184,11 @@ if (CMAKE_COMPILER_IS_GNUCXX)
       # definitely heap allocated.
       add_compile_options(-Wno-free-nonheap-object)
    endif()
+
+   if(${CMAKE_VERSION} VERSION_GREATER "3.8.0") 
+      # strip debug symbols to make the binary smaller
       target_link_options(${target_name} PRIVATE $<$<CONFIG:RELEASE>:-s>)
+   endif()
 
 elseif (MSVC)
    # Treat warnings as errors.
@@ -194,7 +198,11 @@ else() # basically Clang
    add_compile_options(-W -Werror)
    # This is for the comment in face_detection_ex.cpp that says "faces/*.jpg"
    add_compile_options(-Wno-comment)
+
+   if(${CMAKE_VERSION} VERSION_GREATER "3.8.0") 
+      # strip debug symbols to make the binary smaller
       target_link_options(${target_name} PRIVATE $<$<CONFIG:RELEASE>:-s>)
+   endif()
 endif()
 
 

examples/CMakeLists.txt

@@ -106,8 +106,12 @@ target_link_libraries(assignment_learning_ex dlib::dlib)
 macro(add_example name)
    add_executable(${name} ${name}.cpp)
    target_link_libraries(${name} dlib::dlib )
-   # And strip symbols to make your binary smaller if you like.  Certainly not required though.
+
+   if(${CMAKE_VERSION} VERSION_GREATER "3.8.0") 
+   # And strip symbols to make your binary smaller if you like.  Certainly not
+   # required though.
        target_link_options(${name} PRIVATE $<$<CONFIG:RELEASE>:-s>)
+   endif()
 endmacro()
 
 # if an example requires GUI, call this macro to check DLIB_NO_GUI_SUPPORT to include or exclude