Fix caffee2 for LLVM trunk
Summary: LLVM trunk is at 13 now. I'm relaxing the places that only supports up to 12.
Test Plan: Try Sandcastle staging builds.
Reviewed By: ayermolo
Differential Revision: D26227448
fbshipit-source-id: 0b69a9c135b34db4de94b82ee38d2fb1b328888b
