Fix some unittests for 64-bit asm. They were operating on int variables as if they were longs. This was causing asm1_1 to fail when compiled with -O3 because it was overwriting the spilled value of callee-saved register %rbx, which the runtime was using as a pointer value at the time.

module vararg5;
import tango.core.Vararg;
extern(C) int printf(char*, ...);
void func(...)
{
    char[] str = va_arg!(char[])(_argptr);
    {printf("%.*s\n", str.length, str.ptr);}
}
void main()
{
    char[] str = "hello";
    func(str);
}