x11/sessreg: build fails with CLANG in FreeBSD 9.0-PRERELEASE

On a freshly updated box the installation of x11/sessreg fails with the
shown message below.
On all boxes I run with FBSD 9 or 10 (all amd64, CLANG build) the build
and installation works fine.

Since I update the box from 8.2-STABLE to 9.0-PRE last night, cleaning
up all ports and having them rebuilt from scratch, I guess I have a
problem with remnants (or missing compatibility?) in the system.

Where to start looking? ttyslot looks like a base system function.


Regards, thanks in advance,
Oliver

===>  Building for sessreg-1.0.7
/usr/bin/make  all-recursive
Making all in man
  GEN    filenames.sed
  GEN    sessreg.1
  CC     sessreg.o
sessreg.c:281:27: warning: implicit declaration of function 'ttyslot' is
invalid in C99 [-Wimplicit-function-declaration]
                        sysnerr (slot_number = ttyslot (), "ttyslot");
                                               ^
1 warning generated.
  CCLD   sessreg
sessreg.o: In function `main':
sessreg.c:(.text+0x7bf): undefined reference to `ttyslot'
clang: error: linker command failed with exit code 1 (use -v to see
invocation)
*** Error code 1

Stop in /usr/ports/x11/sessreg/work/sessreg-1.0.7.
*** Error code 1

Stop in /usr/ports/x11/sessreg/work/sessreg-1.0.7.
*** Error code 1

Stop in /usr/ports/x11/sessreg/work/sessreg-1.0.7.
*** Error code 1

Stop in /usr/ports/x11/sessreg.