Fix build error on Windows

[dcodeIO]

This PR fixes the compile error seen on Windows as described in #16. Still unable to run the tests, but it compiles and the native module loads with the following exports:

{
  seek: [Function: seek],
  schedYield: [Function: schedYield],
  realtime: [Function: realtime],
  SEEK_SET: 0,
  SEEK_CUR: 1,
  SEEK_END: 2,
  path: 'XY\\node-wasi\\build\\Release\\wasi.node'
}

Instead of running the tests, I tried node run example/cowsay.wasm with some custom logging, which unfortunately yields

fd_prestat_get 3 1048560
 -> 0
fd_prestat_dir_name 3 1114248 1
 -> 0
fd_fdstat_get 3 1048536
 -> 0
fd_prestat_get 4 1048560
 -> 8
environ_sizes_get 1048560 1048572
 -> 0
environ_get 1114280 1114472
 -> 0
args_sizes_get 1048572 1048560
 -> 0
args_get 1114248 1117184
 -> 0
args_sizes_get 1047624 1047628
 -> 0
args_get 1117304 1117320
 -> 0
fd_read 0 1047528 1 1047500
 -> 31
fd_write 2 1048152 1 1048124
 -> 31
fd_write 2 1047816 1 1047788
 -> 31
fd_write 2 1047816 1 1047788
 -> 31

wasm-00401b0a:553

RuntimeError: unreachable
    at __rust_start_panic (wasm-function[552]:1)
    at rust_panic (wasm-function[547]:38)
    at _ZN3std9panicking20rust_panic_with_hook17h12b7239ed4348eaeE (wasm-function[542]:542)
    at _ZN3std9panicking18continue_panic_fmt17hfbe042bfacb6a5d7E (wasm-function[541]:151)
    at _ZN3std9panicking15begin_panic_fmt17hb49e9d7f7ff6a73dE (wasm-function[479]:108)
    at _ZN3std2io5stdio7_eprint17hb2d5f2878b4c5d81E (wasm-function[516]:827)
    at _ZN83_$LT$core..result..Result$LT$$u21$$C$E$GT$$u20$as$u20$std..process..Termination$GT$6report17hd3ad7ac212fc5219E (wasm-function[286]:220)
    at _ZN86_$LT$core..result..Result$LT$$LP$$RP$$C$E$GT$$u20$as$u20$std..process..Termination$GT$6report17h32d24a5b7a33fc9bE (wasm-function[287]:226)
    at _ZN3std2rt10lang_start28_$u7b$$u7b$closure$u7d$$u7d$17h6f5d71df502e16ffE (wasm-function[81]:80)
    at _ZN3std10sys_common9backtrace28__rust_begin_short_backtrace17h1f5c6d3d9bd1f408E (wasm-function[526]:8)

but that looks like it's a different issue - is it?