Fix: correct file name in diagnostics.


git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@172405 91177308-0d34-0410-b5e6-96231b3b80d8
Added a test for clang-format diagnostics.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@172407 91177308-0d34-0410-b5e6-96231b3b80d8