According to gdbm NEW, the dbm/ndbm compatibility routines was moved to
libgdbm_compat in v1.8.1, which was released in late 2002.

The patch works for gdbm-1.8.1+. But I am afraid that the patch will
cause build error with gdbm-1.8.0 and earlier version. A more
sophisticated approach is needed. The approach will do the following:

1. find gdbm library and gdbm/ndbm.h header
2. check the presence of dbm_open() function in gdbm library
3. if present, link with gdbm
4. if not, link with gdbm_compat

Step 1 and 3 are already in setup.py. The patch adds step 4, but step 2
is missing.

I don't have enough skill in distutil to implement it though...