EX_OK collision

[Bruno Haible]

Warning seen on IRIX 6.5:

"///usr/include/unistd.h", line 43: warning(1047): macro redefined differently

IRIX 6.5 has two definitions of EX_OK:
  - one in <unistd.h>, protected with "#if _SGIAPI", as a flag that can be
    passed to the access() function, with value 020,
  - one in <sysexits.h>, always active, as an exit code, with value 0.

Which definition is active, thus depends on the order of inclusion.

What should we do?

  (a) Do nothing.

  (b) Create a replacement <sysexits.h> that does

         #include <unistd.h>
         #undef EX_OK
         #include </usr/include/sysexits.h>

  (c) Create a replacement <unistd.h> that does

         #include </usr/include/unistd.h>
         #undef EX_OK

      and a replacement <sysexits.h> that does

         #include <unistd.h>
         #include </usr/include/sysexits.h>

Which of the three is best? Why?

Bruno