The seeder tests are conditioned to the seeder build, but it must be
built only if the seeder is built *AND* the tests are enabled.
If the tests are not enabled there is no check for the boost unit tests
library.

./autogen.sh
mkdir build && cd build
../configure
make

Check that bitcoin-seeder and test_bitcoin-seeder are built.

../configure --disable-tests
make

Check that bitcoin-seeder is built but not test_bitcoin-seeder.

../configure --without-seeder
make

Check that neither bitcoin-seeder nor test_bitcoin-seeder is built.