[MLton] crossMap

[Stephen Weeks]

> gcc version 4.0 gives the following warning when crossMap is declared as a 
> uchar pointer.
> 
> gc.c: In function createCardMapAndCrossMap:
> gc.c:1272: warning: pointer targets in assignment differ in signedness
> gc.c: In function resizeCardMapAndCrossMap:
> gc.c:2885: warning: pointer targets in assignment differ in signedness
> gc.c:2889: warning: pointer targets in passing argument 2 of copy differ in signedness
> 
> The line 2885 warning should be fixed by declaring oldCrossMap as a uchar 
> pointer, though that simply makes the oldCrossMap argument at line 2889 
> give a warning about different signedness.

I would think these warnings are easily fixed by changing the type of
oldCrossMap and inserting casts at line 1272 and 2888.  I don't have a
gcc 4.0 handy, so could you please check and do the commit if it's OK?