Summary:
Upgrade tool chain to the latest. It is done mostly manually as build_tools/build_detect_platform fails to update many of them.
Try to fix a new clang analyze warning with the new tool chain.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/7251
Test Plan: "make all", "USE_CLANG=1 make all"
Reviewed By: riversand963
Differential Revision: D23091090
fbshipit-source-id: 732e5a30137837431438f85f36296406b641f975
