Isolated emscripten in new lib

lib/emscripten/src/varargs.rs

@@ -0,0 +1,15 @@
+use wasmer_runtime::Instance;
+use std::mem;
+
+#[repr(transparent)]
+pub struct VarArgs {
+    pub pointer: u32, // assuming 32bit wasm
+}
+
+impl VarArgs {
+    pub fn get<T: Sized>(&mut self, instance: &mut Instance) -> T {
+        let ptr = instance.memory_offset_addr(0, self.pointer as usize);
+        self.pointer += mem::size_of::<T>() as u32;
+        unsafe { (ptr as *const T).read() }
+    }
+}