Aside from libkvm.old not knowing about _PATH_KVMDB, I've run into the
following problem: 

Everything in libc compiles happily (once _PATH_KVMDB is defined) but
the shared library apparently contains undefined things of the form
SYS_*, for example running (i think) any dynamically linked program
fails with:

/usr/libexec/ld.so: Undefined symbol "SYS_setreuid" in who:/usr/lib/libc.so.12.7

Among other things this stops "make install" dead in its tracks because
install ceases to function. :)