clang-format: Handle \n the same way as std::endl with stream operator.

clang-format breaks multi-line streams after std::endl.
It now also break for '\n', the suggested replacement for std::endl:

  http://llvm.org/docs/CodingStandards.html#avoid-std-endl

Before:
  llvm::errs() << aaaaaaaaaaaaaaaaaaaaaa << '\n' << bbbbbbbbbbbbbbbbbbbbbb
               << '\n';
  llvm::errs() << aaaa << "aaaaaaaaaaaaaaaaaa\n" << bbbb
               << "bbbbbbbbbbbbbbbbbb\n";

After:
  llvm::errs() << aaaaaaaaaaaaaaaaaaaaaa << '\n'
               << bbbbbbbbbbbbbbbbbbbbbb << '\n';
  llvm::errs() << aaaa << "aaaaaaaaaaaaaaaaaa\n"
               << bbbb << "bbbbbbbbbbbbbbbbbb\n";

This changeset ensure that multiline streams have a line break after:
  - std::endl
  - '\n'
  - "\n"
  - "Some Text\n"

Patch by Jean-Philippe Dufraigne, thank you.

llvm-svn: 256832