ndbm.h and gdbm-compat

[Steven Drake <sbd%NetBSD.org@localhost>]

I've noticed that on Linux systems if gdbm-compat is installed many 
packages fail because they see the /usr/include/ndbm.h and think the 
system has a native ndbm implementation in either libc or libndbm, neither 
of which is true. 

I'm wondering whether there should be an ndbm.buildlink3.mk and
ndbm.builtin.mk as part on the solution or should I just fix individual
packages one by one.

-- 
Steven