[clang-tidy] Fixed header guards using clang-tidy llvm-header-guard check. NFC.

The patch was generated using this command:
$ clang-tidy/tool/run-clang-tidy.py -header-filter=.*clang-tidy.* -fix \
    -checks=-*,llvm-header-guard clang-tidy.*
$ svn revert --recursive clangt-tidy/llvm/
(to revert a few buggy fixes)

llvm-svn: 231669