errors with 8.1 make on Solaris

I'm getting errors at the make stage for 8.1.0 on Solaris 8 despite
configure looking ok. A similar issue was reported with 8.0.3 on Solaris 10
but there didn't seem to be a resolution.
http://archives.postgresql.org/pgsql-admin/2005-09/msg00029.php
make in this instance is gmake.

utils/SUBSYS.o: In function `is_infinite':
: undefined reference to `isinf'
utils/SUBSYS.o: In function `float4in':
: undefined reference to `isinf'
utils/SUBSYS.o: In function `float8in':
: undefined reference to `isinf'
collect2: ld returned 1 exit status
make[2]: *** [postgres] Error 1

./configure --with-python --with-includes=/usr/local/include

Target: sparc-sun-solaris2.8
Configured with: ../configure --cache-file=./config.cache
--srcdir=/d1/ltmp/openpkg-bf/rm8-sparc64-solaris8/TMP/gcc-4.0.2/obj/..
--prefix=/openpkg --exec-prefix =/openpkg --includedir=/openpkg/include/gcc
--libexecdir=/openpkg/libexec/gcc
--with-gxx-include-dir=/openpkg/include/g++
--with-local-prefix=/openpkg/lib/gcc --enable-languages=c,c++
--enable-threads=posix --disable-maintainer-mode --disable-shared
--disable-nls --with-gnu-ld --with-ld=/openpkg/bin/ld --with-gnu-as
--with-as=/openpkg/bin/as
Thread model: posix
gcc version 4.0.2 (OpenPKG-2.5)

Thanks for any help.

Janet Bagg, CSAC, Univ of Kent, UK