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
diff --git a/clang/lib/Format/ContinuationIndenter.cpp b/clang/lib/Format/ContinuationIndenter.cpp
index e7e1366..d81b0f6 100644
--- a/clang/lib/Format/ContinuationIndenter.cpp
+++ b/clang/lib/Format/ContinuationIndenter.cpp
@@ -257,8 +257,10 @@
       Previous.is(tok::l_brace) && !Current.isOneOf(tok::r_brace, tok::comment))
     return true;
 
-  if (Current.is(tok::lessless) && Previous.is(tok::identifier) &&
-      Previous.TokenText == "endl")
+  if (Current.is(tok::lessless) &&
+      ((Previous.is(tok::identifier) && Previous.TokenText == "endl") ||
+       (Previous.Tok.isLiteral() && (Previous.TokenText.endswith("\\n\"") ||
+                                     Previous.TokenText == "\'\\n\'"))))
     return true;
 
   return false;