Fix -Wimplicit-fallthrough warning

Reviewers: EricWF, ldionne, mclow.lists

Reviewed By: ldionne

Subscribers: christof, libcxx-commits

Differential Revision: https://reviews.llvm.org/D54234

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@346369 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed