Changes to runtime.

[Tyson Richard DOWD]

In order to add layout information about stack frames, every entry label
needs to have a stack_layout structure defined for it, and every
internal label needs a similar structure which refers to the entry
label. 

To do this in the .mod files in the runtime, it is simplest to just
stop using .mod files altogether, and instead use .c files.
At the same time, I could pretty easily rename those .c files
to mercury_whatever.c.

Does anyone have any serious objections to this? Would anyone prefer
a particular timing for this change? (merging might become tricky after
the change).

-- 
       Tyson Dowd           #          Another great idea from the 
                            #            people who brought you
      trd at .cs.mu.oz.au      #               Beer Milkshakes!
http://www.cs.mu.oz.au/~trd #	         Confidence --- Red Dwarf