How is the db lib being linked in?  can you post the relevant db parts of
the Config file?

The following is excerpted from a manual build I did on OpenBSD a year or
so ago.

# DB definitions (required if SESSION_CACHE_ENABLE set)
#
# Following suitable for Redhat Linux which has DB 3 preinstalled
DB_INCLUDE=-I ${LOCALPREFIX}/include
DB_LIBS=-L/usr/local/lib -ldb

# Following suitable for FreeBSD with DB 4 package installed
#DB_INCLUDE=-I/usr/local/include/db4
#DB_LIBS=-L/usr/local/lib -ldb4