using the configuration flag --with-db3=/sw

Making all in dba
cc -I. -I/Users/halim/dev/apache/php-4.2.1/ext/dba -I/Users/halim/dev/apache/php-4.2.1/main -I/Users/halim/dev/apache/php-4.2.1 -I/Users/halim/dev/apache/php-4.2.1/Zend -I/sw/include -I/sw/include/libxml2 -I/sw/include/freetype2/freetype -I/Users/halim/dev/apache/php-4.2.1/ext/mysql/libmysql -I/sw/include/pspell  -I/Users/halim/dev/apache/php-4.2.1/TSRM -g -O2  -c dba.c && touch dba.lo
cc -I. -I/Users/halim/dev/apache/php-4.2.1/ext/dba -I/Users/halim/dev/apache/php-4.2.1/main -I/Users/halim/dev/apache/php-4.2.1 -I/Users/halim/dev/apache/php-4.2.1/Zend -I/sw/include -I/sw/include/libxml2 -I/sw/include/freetype2/freetype -I/Users/halim/dev/apache/php-4.2.1/ext/mysql/libmysql -I/sw/include/pspell  -I/Users/halim/dev/apache/php-4.2.1/TSRM -g -O2  -c dba_cdb.c && touch dba_cdb.lo
cc -I. -I/Users/halim/dev/apache/php-4.2.1/ext/dba -I/Users/halim/dev/apache/php-4.2.1/main -I/Users/halim/dev/apache/php-4.2.1 -I/Users/halim/dev/apache/php-4.2.1/Zend -I/sw/include -I/sw/include/libxml2 -I/sw/include/freetype2/freetype -I/Users/halim/dev/apache/php-4.2.1/ext/mysql/libmysql -I/sw/include/pspell  -I/Users/halim/dev/apache/php-4.2.1/TSRM -g -O2  -c dba_db2.c && touch dba_db2.lo
cc -I. -I/Users/halim/dev/apache/php-4.2.1/ext/dba -I/Users/halim/dev/apache/php-4.2.1/main -I/Users/halim/dev/apache/php-4.2.1 -I/Users/halim/dev/apache/php-4.2.1/Zend -I/sw/include -I/sw/include/libxml2 -I/sw/include/freetype2/freetype -I/Users/halim/dev/apache/php-4.2.1/ext/mysql/libmysql -I/sw/include/pspell  -I/Users/halim/dev/apache/php-4.2.1/TSRM -g -O2  -c dba_dbm.c && touch dba_dbm.lo
cc -I. -I/Users/halim/dev/apache/php-4.2.1/ext/dba -I/Users/halim/dev/apache/php-4.2.1/main -I/Users/halim/dev/apache/php-4.2.1 -I/Users/halim/dev/apache/php-4.2.1/Zend -I/sw/include -I/sw/include/libxml2 -I/sw/include/freetype2/freetype -I/Users/halim/dev/apache/php-4.2.1/ext/mysql/libmysql -I/sw/include/pspell  -I/Users/halim/dev/apache/php-4.2.1/TSRM -g -O2  -c dba_gdbm.c && touch dba_gdbm.lo
cc -I. -I/Users/halim/dev/apache/php-4.2.1/ext/dba -I/Users/halim/dev/apache/php-4.2.1/main -I/Users/halim/dev/apache/php-4.2.1 -I/Users/halim/dev/apache/php-4.2.1/Zend -I/sw/include -I/sw/include/libxml2 -I/sw/include/freetype2/freetype -I/Users/halim/dev/apache/php-4.2.1/ext/mysql/libmysql -I/sw/include/pspell  -I/Users/halim/dev/apache/php-4.2.1/TSRM -g -O2  -c dba_ndbm.c && touch dba_ndbm.lo
cc -I. -I/Users/halim/dev/apache/php-4.2.1/ext/dba -I/Users/halim/dev/apache/php-4.2.1/main -I/Users/halim/dev/apache/php-4.2.1 -I/Users/halim/dev/apache/php-4.2.1/Zend -I/sw/include -I/sw/include/libxml2 -I/sw/include/freetype2/freetype -I/Users/halim/dev/apache/php-4.2.1/ext/mysql/libmysql -I/sw/include/pspell  -I/Users/halim/dev/apache/php-4.2.1/TSRM -g -O2  -c dba_db3.c && touch dba_db3.lo
dba_db3.c:46: undefined type, found `DBC'
cpp-precomp: warning: errors during smart preprocessing, retrying in basic mode
dba_db3.c:46: parse error before `DBC'
dba_db3.c:46: warning: no semicolon at end of struct or union
dba_db3.c:47: warning: data definition has no type or storage class
dba_db3.c: In function `dba_open_db3':
dba_db3.c:58: `DB_UNKNOWN' undeclared (first use in this function)
dba_db3.c:58: (Each undeclared identifier is reported only once
dba_db3.c:58: for each function it appears in.)
dba_db3.c:62: `DB_RDONLY' undeclared (first use in this function)
dba_db3.c:63: `DB_CREATE' undeclared (first use in this function)
dba_db3.c:66: `DB_TRUNCATE' undeclared (first use in this function)
dba_db3.c:77: structure has no member named `open'
dba_db3.c:78: invalid operands to binary *
dba_db3.c:81: structure has no member named `dbp'
dba_db3.c:82: structure has no member named `cursor'
dba_db3.c:87: too many arguments to function
dba_db3.c: In function `dba_close_db3':
dba_db3.c:95: `dba' undeclared (first use in this function)
dba_db3.c: In function `dba_fetch_db3':
dba_db3.c:106: `dba' undeclared (first use in this function)
dba_db3.c:107: parse error before `gkey'
dba_db3.c:107: `gkey' undeclared (first use in this function)
dba_db3.c: In function `dba_update_db3':
dba_db3.c:120: `dba' undeclared (first use in this function)
dba_db3.c:121: parse error before `gkey'
dba_db3.c:121: `gkey' undeclared (first use in this function)
dba_db3.c:128: `DB_NOOVERWRITE' undeclared (first use in this function)
dba_db3.c: In function `dba_exists_db3':
dba_db3.c:137: `dba' undeclared (first use in this function)
dba_db3.c:138: parse error before `gkey'
dba_db3.c:138: `gkey' undeclared (first use in this function)
dba_db3.c: In function `dba_delete_db3':
dba_db3.c:149: `dba' undeclared (first use in this function)
dba_db3.c:150: parse error before `gkey'
dba_db3.c:150: `gkey' undeclared (first use in this function)
dba_db3.c: In function `dba_firstkey_db3':
dba_db3.c:157: `dba' undeclared (first use in this function)
dba_db3.c: In function `dba_nextkey_db3':
dba_db3.c:174: `dba' undeclared (first use in this function)
dba_db3.c:175: parse error before `gkey'
dba_db3.c:178: `gkey' undeclared (first use in this function)
dba_db3.c:179: `gval' undeclared (first use in this function)
dba_db3.c:181: `DB_NEXT' undeclared (first use in this function)
dba_db3.c:183: `nkey' undeclared (first use in this function)
dba_db3.c: In function `dba_sync_db3':
dba_db3.c:198: `dba' undeclared (first use in this function)
make[3]: *** [dba_db3.lo] Error 1
make[2]: *** [all-recursive] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all-recursive] Error 1

However...
[localhost:~/dev/apache/php-4.2.1] halim% grep DB_UNKNOWN /sw/include/ -r
/sw/include/db3/db.h:   DB_UNKNOWN=5                    /* Figure it out on open. */