[RFC/AIX] xm-aix4.h - Move some host-specific stuff

[Joel Brobecker <brobecker@gnat.com>]

The last part of config/xm-aix4.h contains the following definitions:

| /* Signal handler for SIGWINCH `window size changed'. */
| 
| #define SIGWINCH_HANDLER  aix_resizewindow
| extern void aix_resizewindow (int);
| 
| /* `lines_per_page' and `chars_per_line' are local to utils.c. Rectify this. */
| #define SIGWINCH_HANDLER_BODY   \
|                                                                         \
| /* Respond to SIGWINCH `window size changed' signal, and reset GDB's    \
|    window settings appropriately. */                                    \
|                                                                         \
| void                                            \
| aix_resizewindow (signo)                        \
|      int signo;                                 \
| {                                               \
|   int fd = fileno (stdout);                     \
|   if (isatty (fd)) {                            \
|     int val;                                    \
|                                                 \
|     val = atoi (termdef (fd, 'l'));             \
|     if (val > 0)                                \
|       lines_per_page = val;                     \
|     val = atoi (termdef (fd, 'c'));             \
|     if (val > 0)                                \
|       chars_per_line = val;                     \
|   }                                             \
| }

Not sure how to handle this part...

First problem: SIGWINCH_HANDLER is used in several files. So when
we define SIGWINCH_HANDLER, we also need to make sure that the prototype
of the procedure it has been defined to is placed somewhere these files
can see them.

Second problem: The body of aix_resizewindow() needs to be moved
somewhere aix-host-specific. Do we have a mechanism for storing
host-specific code? *-nat files, maybe (I wouldn't think so).
Moving that body would allow us to get rid of SIGWINCH_HANDLER_BODY.

If we had a location that would be host-specific to AIX, I would do
the following: Declare in one of .h files a variable, initialized
to NULL, that would be a pointer to the SIGWINCH event. Then, initialize
this variable to aix_resizewindow during the initialization phase
of that aix file. Then modify all the users of this macro from

        #ifdef SIGWINCH_HANDLER
                do_something_with (SIGWINCH_HANDLER);
        #endif

to code like this:

        if (sigwinch_handler != NULL)
           do_something_with (SIGWINCH_HANDLER);

-- 
Joel