regex: /l in combo with others in syn start class

regex: /l in combo with others in syn start class

Now that regexes can be combinations of different charset modifiers,
a synthetic start class can match locale and non-locale both.  locale
should generally match only things in the bitmap for code points < 256.
But a synthetic start class with a non-locale component can match such
code points.  This patch makes an exception for synthetic nodes that
will be resolved if it passes and is matched again for real.