configure: add --without-mdb flag

Add a configuration flag that prevents mdb_v8.so from being built.
The default behavior is still the same and mdb_v8.so is built by default
on Solaris based platforms such as SmartOS.

Using --without-mdb fixes build issues on Solaris based platforms where
libproc.h is not available or not compatible with the one shipped by
SmartOS.

Fixes #6439.

Reviewed-By: Julien Gilli <julien.gilli@joyent.com>
PR-URL: https://github.com/joyent/node/pull/25707