If you get the following error whilst compiling:

In file included from /usr/local/lib/gcc-lib/sparc-sun-solaris2.3/2.6.3/include/sys/user.h:48,
                 from /usr/include/sys/file.h:15,
                 from ../ip_nat.c:15:
/usr/include/sys/psw.h:19: #error Kernel include of psw.h

Remove (comment out) the line in
/usr/local/lib/gcc-lib/sparc-sun-solaris2.3/2.6.3include/sys/user.h
which includes psw.h