tde_create_tarball: SOURCEDIR can be specified as relative.

If the list of files is obtained internally in a macro,
it will be sorted. This prevents unexpected order of files
- improves certainty for reproducible builds.

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit fb4f389731)

modules/TDEMacros.cmake

@@ -2263,8 +2263,13 @@ macro( tde_create_tarball )
     tde_message_fatal( "Target tarball name not specified." )
   endif( )
 
+  if( NOT IS_ABSOLUTE ${_sourcedir} )
+    set( _sourcedir "${CMAKE_CURRENT_SOURCE_DIR}/${_sourcedir}" )
+  endif( )
+
   if( NOT _files )
     file( GLOB_RECURSE _files RELATIVE ${_sourcedir} "${_sourcedir}/*" )
+    list( SORT _files )
   endif( )
 
   unset( _files_deps )