[clang] Move branch-protection from CodeGenOptions to LangOptions

Summary:
Reason: the option has an effect on preprocessing.

Also see thread: http://lists.llvm.org/pipermail/cfe-dev/2020-March/065014.html

Reviewers: chill, efriedma

Reviewed By: efriedma

Subscribers: efriedma, danielkiss, cfe-commits, kristof.beyls

Tags: #clang

Differential Revision: https://reviews.llvm.org/D77131