Things to finish before moving onto compiler optimizations, C extensions, other nice features

- self host. not yet compiling:
    - io.c (TODO varargs)
    - c/eval.c, ir/fold.c (NYI flt -> u64 cvt)
    - c/builtin.c (preprocessor bugs)
    - ir/optmem.c (preprocessor bugs w/ imap macros)
    - embedfilesdir.c (static eval bug)

at some point add another backend like arm64 to make sure the non target specific stuff is generic enough..