create the windows io mod and link printf (#144)

lib/emscripten/src/io/mod.rs

@@ -0,0 +1,11 @@
+#[cfg(unix)]
+mod unix;
+
+#[cfg(windows)]
+mod windows;
+
+#[cfg(unix)]
+pub use self::unix::*;
+
+#[cfg(windows)]
+pub use self::windows::*;

lib/emscripten/src/io/windows.rs

@@ -0,0 +1,29 @@
+use libc::{c_char, c_int};
+use wasmer_runtime_core::vm::Ctx;
+
+// This may be problematic for msvc which uses inline functions for the printf family
+// this cfg_attr will try to link with the legacy lib that does not inline printf
+// this will allow for compiliation, but will produce a linker error if there is a problem
+// finding printf.
+#[cfg_attr(
+    all(windows, target_env = "msvc"),
+    link(name = "legacy_stdio_definitions", kind = "static-nobundle")
+)]
+extern "C" {
+    #[link_name = "printf"]
+    pub fn _printf(s: *const c_char, ...) -> c_int;
+}
+
+/// putchar
+pub fn putchar(chr: i32, ctx: &mut Ctx) {
+    unsafe { libc::putchar(chr) };
+}
+
+/// printf
+pub fn printf(memory_offset: i32, extra: i32, ctx: &mut Ctx) -> i32 {
+    debug!("emscripten::printf {}, {}", memory_offset, extra);
+    unsafe {
+        let addr = emscripten_memory_pointer!(ctx.memory(0), memory_offset) as _;
+        _printf(addr, extra)
+    }
+}