Postgresql 7.4.1 Compile problem for SCO 5.0.5

I am trying to compile postgresql 7.4.1 for sco 5.0.5 and get the following error:

"thread.c", line 269: error: undefined symbol: h_errno

Any ideas?

./configure --with-libs=/usr/local/lib --with-includes=/usr/local/include

herbie!/tmp/postgresql-7.4.1 # gmake
gmake -C doc all
gmake[1]: Entering directory `/tmp/postgresql-7.4.1/doc'
gmake[1]: Nothing to be done for `all'.
gmake[1]: Leaving directory `/tmp/postgresql-7.4.1/doc'
gmake -C src all
gmake[1]: Entering directory `/tmp/postgresql-7.4.1/src'
gmake -C port all
gmake[2]: Entering directory `/tmp/postgresql-7.4.1/src/port'
cc -b elf -O  -I../../src/include -I/usr/local/include  -c thread.c
"thread.c", line 269: error: undefined symbol: h_errno
gmake[2]: *** [thread.o] Error 1
gmake[2]: Leaving directory `/tmp/postgresql-7.4.1/src/port'
gmake[1]: *** [all] Error 2
gmake[1]: Leaving directory `/tmp/postgresql-7.4.1/src'
gmake: *** [all] Error 2
herbie!/tmp/postgresql-7.4.1 #