Summary: Change compiler flag "-Wno-unguarded-availability" to "-Wunguarded-availability" in order to make build time safety check for unsafe newly introduced api without guarding it with available conditional.
Reviewed By: priteshrnandgaonkar
Differential Revision: D20335903
fbshipit-source-id: b4b0e492a9244233f1bc3b5ba2a63c6415c92bb4
72a74c9a1d