[MLton] Windows ports and paths

[Matthew Fluet]

> > The -target-cc-opt stuff is for cross-compiling.
> 
> The -target-{cc,link}-opt stuff is for sending
> target-platform-specific options to gcc.  This happens whether or not
> one is cross compiling.

Agreed, but Wesley's proposal was to eliminate the -target-{cc,link}-opt
options in favor of the shell script pulling in a target specific set of
{cc,link}-opt options based on the determination of host/arch.  I was 
pointing out that the limitation of that approach was that it removes the 
ability to (easily) cross-compile.