With Solaris 7, I installed the gcc version 2.8.1 package from
www.sunfreeware.com.

I downloaded Sleepycat's BerkeleyDB version 2.7.5 from
www.sleepycat.com and followed their web documentation for
installation:  I went to the build_unix directory, then used:
        ../dist/configure
        make
        make install
By default, this created the directory /usr/local/BerkeleyDB...

Once this was installed, I entered the following commands from sh (not csh):
        env \
                ac_cv_func_pthread_create=no ol_cv_kthread_flag=no \
                ol_cv_pthread_flag=no ol_cv_pthreads_flag=no \
                ol_cv_thread_flag=no \
                CPPFLAGS="-I/usr/local/BerkeleyDB/include" \
                LDFLAGS="-L/usr/local/BerkeleyDB/lib" \
        ./configure \
        --with-ldbm-api=db2

After this I was able to continue with "make depend"