Avoid race condition when using multiple make jobs

Avoid race condition when using multiple make jobs

Avoid race condition when symlinking XML files.
When declaring a rule with many files as target, the rule is called
when any of them is requested, resulting in multiple for loops happening
during a make process using more than one job.
Also, use '$(LN_S) -f' rather than removing and recreating a file,
that one should be as supported as 'rm -f' and requires one less command.