[clang-tidy] Fix bug in bugprone-use-after-move check

Summary:
The bugprone-use-after-move check exhibits false positives for certain uses of
the C++17 if/switch init statements. These false positives are caused by a bug
in the ExprSequence calculations.

This revision adds tests for the false positives and fixes the corresponding
sequence calculation.

Reviewers: gribozavr

Subscribers: xazax.hun, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D67292

llvm-svn: 371396