Update berkeley-db prefix search for osx

Summary:
Since upgrading to berkeley-db >5.3, we now need to search
for a different prefix. Update configure.ac to do so.

Test Plan: run configure and build

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1797