clang-format: fix prefix for doxygen comments after member

Summary:
Doxygen supports putting documentation blocks after member, by adding
an additional < marker in the comment block. This patch makes sure
this marker is used in lines which are introduced by breaking the
comment.

  int foo; ///< Some very long comment.

becomes:

  int foo; ///< Some very long
           ///< comment.

Contributed by @Typz!

Reviewers: krasimir

Reviewed By: krasimir

Subscribers: djasper, klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D33282

llvm-svn: 303330
diff --git a/clang/lib/Format/BreakableToken.cpp b/clang/lib/Format/BreakableToken.cpp
index c97486e..f70597c 100644
--- a/clang/lib/Format/BreakableToken.cpp
+++ b/clang/lib/Format/BreakableToken.cpp
@@ -41,7 +41,8 @@
 }
 
 static StringRef getLineCommentIndentPrefix(StringRef Comment) {
-  static const char *const KnownPrefixes[] = {"///", "//", "//!"};
+  static const char *const KnownPrefixes[] = {
+      "///<", "//!<", "///", "//", "//!"};
   StringRef LongestPrefix;
   for (StringRef KnownPrefix : KnownPrefixes) {
     if (Comment.startswith(KnownPrefix)) {
@@ -692,6 +693,10 @@
           Prefix[i] = "/// ";
         else if (Prefix[i] == "//!")
           Prefix[i] = "//! ";
+        else if (Prefix[i] == "///<")
+          Prefix[i] = "///< ";
+        else if (Prefix[i] == "//!<")
+          Prefix[i] = "//!< ";
       }
 
       Tokens[i] = LineTok;