839add193b build: Enable -Wsuggest-override (Hennadii Stepanov)
de5e91c303 refactor: Add BerkeleyDatabaseVersion() function (Hennadii Stepanov)
Pull request description:
From GCC [docs](https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/Warning-Options.html):
> `-Wsuggest-override`
> Warn about overriding virtual functions that are not marked with the override keyword.
~This PR is based on #16722 (the first commit).~ See: https://github.com/bitcoin/bitcoin/pull/16722#issuecomment-584111086
ACKs for top commit:
fanquake:
ACK 839add193b
vasild:
ACK 839add193
practicalswift:
ACK 839add193b assuming Travis is happy: patch looks correct
Tree-SHA512: 1e8cc085da30d41536deff9b181962c1882314ab252c2ad958294087ae1e5a0dfa4886bdbe36f21cf6ae71df776a8420f349f007d4b5b49fd79ba98ce308965a