Only optimize release builds (not debug builds).
Only optimize release builds (not debug builds).

-flto is really slow, especially on ARM, and it takes enough RAM that
density fails on some lower-memory machines unless I add swap space.

Signed-off-by: Evan Nemerson <178b62e73cc3fab9e30bf27b2372c9ff92401915@nemerson.com>

Cloudef/squash,Cloudef/squash,wolut/squash,quixdb/squash,Cloudef/squash,wolut/squash,quixdb/squash,quixdb/squash,jibsen/squash,jibsen/squash,jibsen/squash,wolut/squash