enable clang warning float-conversion
enable clang warning float-conversion

Summary: Enable it as an error and fix all resulting build failures in folly.

Reviewed By: luciang

Differential Revision: D33838564

fbshipit-source-id: 13130e4b9c090db6a4ec7c8fcd150d6aa9c000b9

facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst