[Driver] Don't remove non-regular files that were outputs.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@173215 91177308-0d34-0410-b5e6-96231b3b80d8
clang/test/Driver/output-file-is-dir.c: This requires shell due to 'cd'.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@173218 91177308-0d34-0410-b5e6-96231b3b80d8