Don't use '-Werror-nondeterministic-tags' with '-T, --tags'.

Don't use '-Werror-nondeterministic-tags' with '-T, --tags'.

If tags are explicitly enabled, re2c should always fail with error
on nondeterministic tags. There's no good in '-Werror-nondeterministic-tags'
diagnostic --- the user cannot reset it anyway.

This commit fixes unsuccessful attempt 2bfe75d57c71c7102dd6e7b4e5f7139411c7c080
"Restore user warnings after temporarily enforcing a warning.", which
resulted in hiding tag errors if '-Wnondeterministic-tags' is not set.