va_arg bug

clang.out

$ clang vatest.c
$ ./a.out
Type is 0
Value is 5
Type is 1
Value is 12
Type is 2
Value is 19
Type is 3
Value is 26
Type is 4
Value is 33

emcc.out

$ emcc vatest.c
clang: warning: argument unused during compilation: '-nostdinc++'
vatest.c:25:17: error: cannot compile this aggregate va_arg expression yet
    print_value(va_arg(ap, mrb_value));
                ^~~~~~~~~~~~~~~~~~~~~
/Users/rafael/develop/webruby/modules/emscripten/system/include/libc/stdarg.h:35:29: note: expanded from macro 'va_arg'
#define va_arg(ap, type)    __builtin_va_arg(ap, type)
                            ^~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
ERROR    emcc: compiler frontend failed to generate LLVM bitcode, halting

vatest.c

#include <stdio.h>
#include <stdarg.h>

typedef struct mrb_value {
  union {
    float f;
    void *p;
    int i;
    short sym;
  } value;
  unsigned tt;
} mrb_value;

void print_value(mrb_value val)
{
  printf("Type is %d\n", val.tt);
  printf("Value is %d\n", val.value.i);
}

void print_list(int n, va_list ap)
{
  int i;

  for (i = 0; i < n; i++) {
    print_value(va_arg(ap, mrb_value));
  }
}

void print_variable_length(int n, ...)
{
  va_list ap;
  va_start(ap, n);
  print_list(n, ap);
  va_end(ap);
}

int main ()
{
  mrb_value values[5];
  int i;

  for (i = 0; i < 5; i++) {
    values[i].tt = i;
    values[i].value.i = i * 7 + 5;
  }

  print_variable_length(5, values[0], values[1], values[2], values[3], values[4]);

  return 0;
}