I enclose you the file unistd.h. It isn't the same tha OSX10.3.
I have tested you indications, and now I can 'make' the source code. What
have changed from 10.3 to 10.4 that breaks this compilation ?
Please send me a copy of your /usr/include/unistd.h file.
In any case, what it means is that your unistd.h file defines
_POSIX_PRIORITY_SCHEDULING but then the functions to support that are
not to be found on the system in the usual places.
You can work around this problem by running ./configure and then editing
port.h and removing the line that says HAS_POSIXSCHED.