[Bug target/44002] need to #include unistd.h for pid_t on alpha-dec-vms

[Bug target/44002] need to #include unistd.h for pid_t on alpha-dec-vms

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=44002

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2024-03-31
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---

POSIX defines pid_t in sys/types.h
(https://pubs.opengroup.org/onlinepubs/009604499/basedefs/sys/types.h.html)


But the way AC_TYPE_PID_T works, is pid_t if incldued in the standard
ac_includes don't define it. 

standard includes in the version of autoconf that is currently used are:
```
#ifdef HAVE_SYS_TYPES_H
# include <sys/types.h>
#endif
....
#ifdef HAVE_UNISTD_H
# include <unistd.h>
#endif"
```

Looks like vms defines it in unistd.h from what I could find on the internet.

So confirmed. Though I am not 100% sure if building for VMS is still supported.