Revert "FileEntry: Remove unused and half-broken copy ctor."

Looks like libstdc++ 4.7 still needs it.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@202896 91177308-0d34-0410-b5e6-96231b3b80d8
[C++11] Simplify a callback to use a lambda.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@202897 91177308-0d34-0410-b5e6-96231b3b80d8