Install symlinks for 'common' files as relative.

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>

template/commonCMakeLists.txt

@@ -3,7 +3,7 @@
 #  (C) 2013 Alexander Golubev (Fat-Zer)
 #  fatzer2 (AT) gmail.com
 #
-#  (C) 2020 Slávek Banko
+#  (C) 2020-2022 Slávek Banko
 #  slavek.banko (AT) axis.cz
 #
 #  Improvements and feedback are welcome
@@ -12,7 +12,7 @@
 #
 #################################################
 
-cmake_minimum_required( VERSION 2.8.12 )
+cmake_minimum_required( VERSION 3.1 )
 
 
 ##### general package setup #####################
@@ -97,8 +97,12 @@ if( BUILD_DOC )
       endforeach( )
     endif()
     foreach( _file IN LISTS common_docs_LINK )
+      file( RELATIVE_PATH _common_link_target
+        "${HTML_INSTALL_DIR}/${_lang}/common"
+        "${TDE_HTML_DIR}/en/common/${_file}"
+      )
       tde_install_symlink(
-        ${TDE_HTML_DIR}/en/common/${_file}
+        ${_common_link_target}
         ${HTML_INSTALL_DIR}/${_lang}/common/${_file}
       )
     endforeach( )