[RFC/AIX] xm-aix4.h - get rid of #undef fd_set & select #include

[Joel Brobecker <brobecker@gnat.com>]

config/xm-aix4.h contains the following definitions:

| /* The following text is taken from config/rs6000.mh:
|  * # The IBM version of /usr/include/rpc/rpc.h has a bug -- it says
|  * # `extern fd_set svc_fdset;' without ever defining the type fd_set.
|  * # Unfortunately this occurs in the vx-share code, which is not configured
|  * # like the rest of GDB (e.g. it doesn't include "defs.h").
|  * # We circumvent this bug by #define-ing fd_set here, but undefining it in
|  * # the xm-rs6000.h file before ordinary modules try to use it.  FIXME, IBM!
|  * MH_CFLAGS='-Dfd_set=int'
|  * So, here we do the undefine...which has to occur before we include
|  * <sys/select.h> below.
|  */
| #undef fd_set
| 
| #include <sys/select.h>

On our systems (AIX 4.3.2 and 5.1), this type is defined in time.h

    typedef struct
    #ifdef _ALL_SOURCE
    fd_set
    #endif /* _ALL_SOURCE */
    {
      long fds_bits[__NUM_ENTRIES];  /* bitmask for open file descriptors */
    } fd_set;

I couldn't find config/rs6000.mh, nor the original comment. So I wonder
if we wouldn't be able to delete these two.

I can give it a try, but would I miss something?

-- 
Joel