Build fix for Visual Studio

[syoyo]

minilisp is great!

And I made a patch making it work on Windows + Visual Studio 2013.

[andrewchambers]

It might be better to just have a windows branch to keep the main code tidy.

[rui314]

I agree with @andrewchambers. This patch is not actually bad, but the spirit of this interpreter is (extreme) minimalism, so we don't want to have #ifdefs in the code.

[larkmjc]

if you want to keep the code simple then you might just use malloc/free unconditionally and not include <sys/mman.h> because you would then be standard C compatible and that is the simplest. but I understand why you might prefer to use mmap/munmap because the system allocator may not remove the footprint of freed memory. you have more precise control using mmap/munmap. in any case I made a slightly different patch in my windows branch to use VirtualAlloc/VirtualFree. it adds a dealloc_semispace to match the alloc_semispace but i'm guessing you won't like it as it also has some #ifdef.

larkmjc@d1cb514

if you don't want to use #ifdef then wouldn't you want to eliminate the preprocessor altogether? it's a pity you can't rely on adjacent stack variables being physically adjacent because then you could just wire root to point to the first frame variable and you wouldn't need the DEFINE macros.