[MLton] MLNLFFI doesn't link on MinGW(?)

[Vesa Karvonen]

Quoting Matthew Fluet <fluet at cs.cornell.edu>:
[...]
> I've never used the Cygwin port extensively or used the MinGW port at all. 
[...]

Just to clarify/FYI, aside from the dl* stuff, mlnlffi[gen] with -linkage
static seems to work on MinGW.  I haven't done *extensive* testing, but the
few simple tests I made seemed to work correctly.

BTW, on my Windows work laptop the MinGW version of the MLton *compiler*
seems to perform noticeably better than the Cygwin version.  In particular,
the Cygwin version seems to use much more memory (which probably slows it
down and even causes it to fail on big enough programs).  I haven't done
any systematic compiler performance testing, however.

-Vesa Karvonen