[CFLAA] Move FunctionHandle to llvm::cflaa.

Also, while here, remove an unneeded `using namespace llvm`.
Thanks to George for the suggestion.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306355 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed