C FFI

[Stephen Weeks]

> One question: what is the easiest to support the C
> foreign function interface from native-code?  Will ld handle
> this easily?

For C functions, we will need to generate the appropriate C calling
convention, which is pretty simple.  It should be easy enough to
figure out from looking at a few 'gcc -S' examples.

For stuff that is currently handled via C #defines, the backend will
need to know about them and generate the correct code on a case by
case basis.