HOWTO: sudo port install db4 Successfully

As Admin: vi /opt/local/var/macports/sources/rsync.macports.org/release/ports/databases/db4/Portfile
Change the line:
configure.args --enable-compat185 --enable-dump185 --enable-cxx \
TO
configure.args --enable-cxx \

Then: sudo port clean db4; sudo port install db4

Background, for those interested:

The db4 package in MacPorts is - as of this writing - broken. It fails to compile due to issues with db_dump18:
> sudo port -b install db4
--->  Fetching db4
--->  Verifying checksum(s) for db4
--->  Extracting db4
--->  Applying patches to db4
--->  Configuring db4
--->  Building db4 with target all
Error: Target org.macports.build returned: shell command " cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_ports_databases_db4/work/db-4.3.29/build_unix" && make all " returned error 2
Command output: ar cru .libs/libdb_tcl-4.3.a  tcl_compat.o tcl_db.o tcl_db_pkg.o tcl_dbcursor.o tcl_env.o tcl_internal.o tcl_lock.o tcl_log.o tcl_mp.o tcl_rep.o tcl_seq.o tcl_txn.o tcl_util.o db185.o mut_tas.o bt_compare.o bt_conv.o bt_curadj.o bt_cursor.o bt_delete.o bt_method.o bt_open.o bt_put.o bt_rec.o bt_reclaim.o bt_recno.o bt_rsearch.o bt_search.o bt_split.o bt_stat.o bt_upgrade.o btree_auto.o hash.o hash_auto.o hash_conv.o hash_dup.o hash_meta.o hash_method.o hash_open.o hash_page.o hash_rec.o hash_reclaim.o hash_stat.o hash_upgrade.o hash_verify.o qam.o qam_auto.o qam_conv.o qam_files.o qam_method.o qam_open.o qam_rec.o qam_stat.o qam_upgrade.o qam_verify.o rep_auto.o rep_backup.o rep_method.o rep_record.o rep_region.o rep_stat.o rep_util.o db_ovfl_vrfy.o db_vrfy.o db_vrfyutil.o bt_verify.o aes_method.o crypto.o mt19937db.o rijndael-alg-fst.o rijndael-api-fst.o crdel_auto.o crdel_rec.o db.o db_am.o db_auto.o db_byteorder.o db_cam.o db_conv.o db_dispatch.o db_dup.o db_err.o db_getlong.o db_idspace.o db_iface.o db_join.o db_log2.o db_meta.o db_method.o db_open.o db_overflow.o db_pr.o db_rec.o db_reclaim.o db_rename.o db_remove.o db_ret.o db_salloc.o db_setid.o db_setlsn.o db_shash.o db_stati.o db_truncate.o db_upg.o db_upg_opd.o dbm.o dbreg.o dbreg_auto.o dbreg_rec.o dbreg_stat.o dbreg_util.o env_file.o env_method.o env_open.o env_recover.o env_region.o env_stat.o fileops_auto.o fop_basic.o fop_rec.o fop_util.o hash_func.o hmac.o hsearch.o lock.o lock_deadlock.o lock_id.o lock_list.o lock_method.o lock_region.o lock_stat.o lock_timer.o lock_util.o log.o log_archive.o log_compare.o log_get.o log_method.o log_put.o log_stat.o mp_alloc.o mp_bh.o mp_fget.o mp_fmethod.o mp_fopen.o mp_fput.o mp_fset.o mp_method.o mp_region.o mp_register.o mp_stat.o mp_sync.o mp_trickle.o mutex.o os_abs.o os_alloc.o os_clock.o os_config.o os_dir.o os_errno.o os_fid.o os_fsync.o os_handle.o os_id.o os_map.o os_method.o os_oflags.o os_open.o os_region.o os_rename.o os_root.o os_rpath.o os_rw.o os_seek.o os_sleep.o os_spin.o os_stat.o os_tmpdir.o os_truncate.o os_unlink.o sha1.o seq_stat.o sequence.o snprintf.o txn.o txn_auto.o txn_method.o txn_rec.o txn_recover.o txn_region.o txn_stat.o txn_util.o xa.o xa_db.o xa_map.o
ranlib: file: .libs/libdb_tcl-4.3.a(tcl_compat.o) has no symbols
ranlib: file: .libs/libdb_tcl-4.3.a(tcl_lock.o) has no symbols
ranlib: file: .libs/libdb_tcl-4.3.a(tcl_log.o) has no symbols
ranlib: file: .libs/libdb_tcl-4.3.a(tcl_rep.o) has no symbols
ranlib: file: .libs/libdb_tcl-4.3.a(snprintf.o) has no symbols
ranlib .libs/libdb_tcl-4.3.a
ranlib: file: .libs/libdb_tcl-4.3.a(tcl_compat.o) has no symbols
ranlib: file: .libs/libdb_tcl-4.3.a(tcl_lock.o) has no symbols
ranlib: file: .libs/libdb_tcl-4.3.a(tcl_log.o) has no symbols
ranlib: file: .libs/libdb_tcl-4.3.a(tcl_rep.o) has no symbols
ranlib: file: .libs/libdb_tcl-4.3.a(snprintf.o) has no symbols
creating libdb_tcl-4.3.la
(cd .libs && rm -f libdb_tcl-4.3.la && ln -s ../libdb_tcl-4.3.la libdb_tcl-4.3.la)
/bin/sh ./libtool --mode=compile /usr/bin/gcc-4.0 -c -O2  -I../dist/.. -I/opt/local/include ../dist/../db_dump185/db_dump185.c
 /usr/bin/gcc-4.0 -c -O2 -I../dist/.. -I/opt/local/include ../dist/../db_dump185/db_dump185.c  -fno-common -DPIC -o .libs/db_dump185.o
../dist/../db_dump185/db_dump185.c: In function 'main':
../dist/../db_dump185/db_dump185.c:212: warning: assignment makes pointer from integer without a cast
../dist/../db_dump185/db_dump185.c:214: warning: assignment makes pointer from integer without a cast
../dist/../db_dump185/db_dump185.c:229: error: 'struct __db' has no member named 'seq'
../dist/../db_dump185/db_dump185.c:229: error: 'R_NEXT' undeclared (first use in this function)
../dist/../db_dump185/db_dump185.c:229: error: (Each undeclared identifier is reported only once
../dist/../db_dump185/db_dump185.c:229: error: for each function it appears in.)
../dist/../db_dump185/db_dump185.c:234: error: 'struct __db' has no member named 'seq'
../dist/../db_dump185/db_dump185.c: In function 'db_hash':
../dist/../db_dump185/db_dump185.c:262: error: 'struct __db' has no member named 'internal'
../dist/../db_dump185/db_dump185.c:264: error: 'struct __db' has no member named 'internal'
../dist/../db_dump185/db_dump185.c: In function 'db_btree':
../dist/../db_dump185/db_dump185.c:289: error: 'struct __db' has no member named 'internal'
make: *** [db_dump185.lo] Error 1

Digging on the DarwinPorts and Fink forums online (usually a goldmine for fixing issues like this) proved fruitless until I looked on the comp.databases.berkeley-db newsgroup and found that the thorn in the compiler's side was an optional component. At that point I had to dig up the MacPorts Portfile for db4 and manually remove the db_compat185 and db_dump185 options from configure.args. Cleaning and rebuilding solved my problem.