[Tooling] Recognize angle brackets for main header

[drdanz]

Summary

clang-format does not recognize as main header an include that uses
angle brackets. This is a common practice used in many projects.

This patch removes the initial check for the '"' character.

clang/lib/Tooling/Inclusions/HeaderIncludes.cpp

if (CategoryRegexs[i].match(IncludeName)) {
         Ret = Style.IncludeCategories[i].Priority;
       break;
     }
   if (CheckMainHeader && IsMainFile && Ret > 0 && isMainHeader(IncludeName))
     Ret = 0;
   return Ret;
 }
 bool IncludeCategoryManager::isMainHeader(StringRef IncludeName) const {
-  if (!IncludeName.startswith("\""))
-    return false;
   StringRef HeaderStem =
       llvm::sys::path::stem(IncludeName.drop_front(1).drop_back(1));
   if (FileStem.startswith(HeaderStem) ||
       FileStem.startswith_lower(HeaderStem)) {
     llvm::Regex MainIncludeRegex(HeaderStem.str() + Style.IncludeIsMainRegex,
                                  llvm::Regex::IgnoreCase);
     if (MainIncludeRegex.match(FileStem))
       return true;