[MLton] bool array size

[Henry Cejtin]

What a shame.  Clearly it really should be fixed.  If I have a chance, I will
try to see if I can understand enough to do it.

As to the array stuff I was talking about, I remember that at least with the
previous release, any array with elements that were not int, word, real and
perhaps char, Word8.word or bool, then the array would consist of pointers
to tuples.  If this was done for bools, and if they all pointed to the same
true and false, then you would again get 4 bytes per element (since only the
pointer would be used).