enable link-time optimization (LTO) for rocksdb library (#15082)
enable link-time optimization (LTO) for rocksdb library (#15082)

* enable link-time optimization (LTO) for rocksdb library

* use IPO_ENABLED from top-level CMakeLists.txt
wiltonlazary/arangodb,arangodb/arangodb,wiltonlazary/arangodb,wiltonlazary/arangodb,arangodb/arangodb,arangodb/arangodb,arangodb/arangodb,wiltonlazary/arangodb,wiltonlazary/arangodb,wiltonlazary/arangodb,arangodb/arangodb,arangodb/arangodb,wiltonlazary/arangodb,wiltonlazary/arangodb,arangodb/arangodb,arangodb/arangodb