Increased usability of the dlib CMakeLists.txt file slightly.

dlib/CMakeLists.txt

@@ -199,6 +199,8 @@ if (NOT DLIB_ISO_CPP_ONLY)
          get_filename_component(sqlite_path2 ${sqlite_path} PATH CACHE)
          include_directories(${sqlite_path2})
          set(dlib_needed_libraries ${dlib_needed_libraries} ${sqlite} )
+      else()
+         set(DLIB_LINK_WITH_SQLITE3 OFF CACHE STRING ${DLIB_LINK_WITH_SQLITE3_STR} FORCE )
       endif()
       mark_as_advanced(sqlite sqlite_path sqlite_path2)
    endif()
@@ -214,13 +216,13 @@ include(TestForSTDNamespace)
 include(TestForANSIStreamHeaders)
 
 
-if (DLIB_LINK_WITH_LIBPNG)
+if (DLIB_LINK_WITH_LIBPNG AND NOT DLIB_ISO_CPP_ONLY)
    add_global_define(DLIB_PNG_SUPPORT)
 else()
    remove_global_define(DLIB_PNG_SUPPORT)
 endif()
 
-if (DLIB_LINK_WITH_LIBJPEG)
+if (DLIB_LINK_WITH_LIBJPEG AND NOT DLIB_ISO_CPP_ONLY)
    add_global_define(DLIB_JPEG_SUPPORT)
 else()
    remove_global_define(DLIB_JPEG_SUPPORT)