js->c calling bugs in ASM_JS mode

asmjs-test.c

#include <stdio.h>

#include <emscripten/emscripten.h>

void EMSCRIPTEN_KEEPALIVE c_func_calling_from_js() {
  printf("This is a c function calling from js!");
}

extern void js_func();

int main(int argc, char *argv[])
{
  js_func();
  return 0;
}

asmjs-test.js

mergeInto(LibraryManager.library, {
  js_func: function() {
    Module.print("Now we are in js side, let's call back to c side!");
    _c_func_calling_from_js();
  }
});

asmjs.out

$ emcc --js-library asmjs-test.js asmjs-test.c -s ASM_JS=1
$ node a.out.js
Now we are in js side, let's call back to c side!

/Users/rafael/develop/tmp/asmjs/a.out.js:1928
      _c_func_calling_from_js();
      ^
ReferenceError: _c_func_calling_from_js is not defined
    at _js_func (/Users/rafael/develop/tmp/asmjs/a.out.js:1928:7)
    at Object._main (/Users/rafael/develop/tmp/asmjs/a.out.js:2444:8)
    at Object.callMain (/Users/rafael/develop/tmp/asmjs/a.out.js:2530:25)
    at doRun (/Users/rafael/develop/tmp/asmjs/a.out.js:2562:20)
    at run (/Users/rafael/develop/tmp/asmjs/a.out.js:2586:12)
    at /Users/rafael/develop/tmp/asmjs/a.out.js:2608:13
    at Object.<anonymous> (/Users/rafael/develop/tmp/asmjs/a.out.js:2625:4)
    at Module._compile (module.js:449:26)
    at Object.Module._extensions..js (module.js:467:10)
    at Module.load (module.js:356:32)

normal.out

$ emcc --js-library asmjs-test.js asmjs-test.c
$ node a.out.js
Now we are in js side, let's call back to c side!
This is a c function calling from js!