[clang-offload-bundler] Fix some Clang-tidy modernize-use-override and Include What You Use warnings; other minor fixes.

Differential revision: https://reviews.llvm.org/D24165



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@280828 91177308-0d34-0410-b5e6-96231b3b80d8