project_file.mako: handle non-ASCII directory names

For GitHub issue #643

langkit/templates/project_file.mako

@@ -81,9 +81,14 @@ library project ${lib_name} is
    ## no simple setup is possible, and this reduces the number of places that
    ## have to worry about these things to this Mako template and to the
    ## langkit.coverage module.
-   Primary_Source_Dirs :=
-     (${', '.join(ascii_repr(emitter.path_to(d, project_path))
-                  for d in source_dirs if d)});
+   Primary_Source_Dirs := (${', '.join(
+       ## GPR tools expect UTF-8 project files (i.e. the default encoding for
+       ## rendered template in Langkit), and we cannot use bytes_repr to format
+       ## the corresponding string literals, as bytes_repr assumes Ada
+       ## (``Character'Val (1)`` is invalid in the GPR world).
+       '"{}"'.format(emitter.path_to(d, project_path).replace('"', '""'))
+       for d in source_dirs if d
+   )});
 
    % if emitter.coverage:
       Secondary_Source_Dirs :=