PATCH: Spell exp2l correctly

[Roland McGrath]

Ok, since long-double-fcts is only set in a few configurations, it turns
out to be pretty easy to tell which ones might be affected.  i.e., it's
only those few long-double-fcts=yes platforms that had it correct.  So,
it's straightforward to add a Versions fragment for each of those few and
update the generic one used by all other configurations.  I've committed
changes to do this.  But I have not actually done a build on any of the
platforms on which sysdeps/generic/w_exp2.c was being used to define exp2l
(or fail to).


Thanks,
Roland