c++ version of twothreads example

Hi Peter,

Try adding the word "externC" before the cyg_user_start function in twothreads.cxx, like this:

/* we install our own startup routine which sets up threads */
externC void cyg_user_start(void)
{
  diag_printf(" Entering\n");
  ...
  ...
}

This should help the linker recognise that you have provided a copy of cyg_user_start, otherwise it will link in the default version. I think externC stops the C++ name-mangler from changing the function name into one that won't link with the code that expects cyg_user_start to be in a module written in C.

Mike