regcomp.c: Don't set /i in start class unless /l

regcomp.c: Don't set /i in start class unless /l

There is a deficiency in the optimizer in which it doesn't get rid of
flags that it should.  One of these is if it should match /i or not.
Currently it always (perhaps not quite, I don't know) assumes that it
should match under /i, yielding false positives and slowing things down.
But a recent commit changed the flag that tells it to do this, so that it
only gets set if /l is also specified.  There is already existing code to
work around the optimizer deficiency for /l.  This commit just moves the
/i flag handling to that existing code, so it won't get invoked unless
/l is specified.