[clang-move] Add header guard for the new header.

Summary:
The header guard generated by clang-move isn't always a perfect
style, just avoid getting the header included multiple times during
compiling period.

Also, we can use llvm-Header-guard clang-tidy check to correct the guard
automatically.

Reviewers: ioeric

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D25610

llvm-svn: 284233