Fix installed CMake targets when DLIB_ISO_CPP_ONLY (#595) (#597)

dlib/CMakeLists.txt

@@ -673,11 +673,7 @@ if (NOT TARGET dlib)
       else()
          add_library(dlib STATIC ${source_files} )
       endif()
-      target_include_directories(dlib
-                                 INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/..>
-                                 INTERFACE $<INSTALL_INTERFACE:include>
-                                 PUBLIC ${dlib_needed_includes}
-                                 )
+      target_include_directories(dlib PUBLIC ${dlib_needed_includes})
       target_link_libraries(dlib PRIVATE ${dlib_needed_libraries})
       if (DLIB_IN_PROJECT_BUILD)
          target_compile_options(dlib PUBLIC ${active_preprocessor_switches})
@@ -692,17 +688,24 @@ if (NOT TARGET dlib)
             add_library(dlib_shared SHARED ${source_files} )
             add_dependencies(dlib_shared dlib)
          endif()
-         target_include_directories(dlib_shared
-                                    INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/..>
-                                    INTERFACE $<INSTALL_INTERFACE:include>
-                                    PUBLIC ${dlib_needed_includes}
-                                    )
+         target_include_directories(PUBLIC ${dlib_needed_includes})
          target_link_libraries(dlib_shared PRIVATE ${dlib_needed_libraries})
          target_compile_options(dlib_shared PRIVATE ${active_preprocessor_switches})
       endif()
 
    endif ()  ##### end of if NOT DLIB_ISO_CPP_ONLY ##########################################################
 
+   # Add source or headers to include directory, for building or installation respectively
+   target_include_directories(dlib
+                              INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/..>
+                              INTERFACE $<INSTALL_INTERFACE:include>
+                              )
+   if (UNIX AND NOT DLIB_IN_PROJECT_BUILD)
+         target_include_directories(dlib_shared
+                                    INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/..>
+                                    INTERFACE $<INSTALL_INTERFACE:include>
+                                    )
+   endif()
    # Allow the unit tests to ask us to compile the all/source.cpp file just to make sure it compiles.
    if (DLIB_TEST_COMPILE_ALL_SOURCE_CPP)
       ADD_LIBRARY(dlib_all_source_cpp STATIC all/source.cpp)