[MLton] Compiling mlton on MacOS

[John Reppy]

I made some progress on the port, before hitting an MLRISC bug in SML/NJ
(I hope to get that fixed for 110.45).  Do you want my diffs so far, or 
do you
want to wait until I get a working version?

There are a couple of things that I think could be improved in the 
porting
process.  One is that you should move to testing features instead of 
operating
system in your header files.  For example, for this 
MLton_Rlimit_virtualMemorySize
constant, the test is

	#if (defined (__FreeBSD__) || defined (__NetBSD__) || 
defined(__APPLE__))
	#define MLton_Rlimit_virtualMemorySize RLIMIT_DATA
	#elif (defined (__CYGWIN__) || defined (__linux__) || defined 
(__sun__))
	#define MLton_Rlimit_virtualMemorySize RLIMIT_AS
	#else
	#error MLton_Rlimit_virtualMemorySize not defined
	#endif

when the following would be more robust

	#if defined(RLIMIT_AS)
	#define MLton_Rlimit_virtualMemorySize RLIMIT_AS
	#elif defined(RLIMIT_DATA
	#define MLton_Rlimit_virtualMemorySize RLIMIT_DATA
	#else
	#error MLton_Rlimit_virtualMemorySize not defined
	#endif

In the long run, I think that you should consider using autoconf.

Also, the files bin/platform and build/lib/platform are identical.  Do 
you really
need both?

	- John