build: add missing leveldb defines
src/leveldb/build_detect_platform shows how upstream defines them. These platform may not be able to fully build or run Bitcoin, but defining all known to leveldb saves future hassle. Now that all possible platforms are enumerated, specifying an unknown one is an error.
Backport of core PR13659
Reviewers: #bitcoin_abc, deadalnix, jasonbcox
Reviewed By: #bitcoin_abc, jasonbcox
Differential Revision: https://reviews.bitcoinabc.org/D3817