Frontend: Add -f{,no-}implicit-modules-uses-lock and -Rmodule-lock

Add -cc1 flags `-fmodules-uses-lock` and `-fno-modules-uses-lock` to
allow the lock manager to be turned off when building implicit modules.

Add `-Rmodule-lock` so that we can see when it's being used.

Differential Revision: https://reviews.llvm.org/D95583