[clang-format] add support for branch attribute macros

[MyDeveloperDay]

Summary

https://github.com/llvm/llvm-project/issues/49184

clang-format doesn't handle the use of AttributeMacros where [[unlikely]] / [[likely]] could be used in if statements

This was nor covered in the original commit {D80144: [clang-format] @lefticus just taught the world how to use [[unlikely]] but we forgot to teach clang-format}

if (StartIndex == End)
    BRANCH_UNLIKELY
return npos;

Give better support via

if (StartIndex == End) [[unlikely]]
  return npos;

if (StartIndex == End) [[unlikely]] {
  return npos;
}

if (StartIndex == End) UNLIKELY
  return npos;

if (StartIndex == End) UNLIKELY {
  return npos;
}

Fixes #49184

[curdeius]

LGTM!

Tested locally.
Has Bolt landed? It seems that the CI adds bolt as the project but it isn't recognized...

clang/lib/Format/UnwrappedLineParser.cpp

 
 void UnwrappedLineParser::parseIfThenElse() {
   assert(FormatTok->Tok.is(tok::kw_if) && "'if' expected");
   nextToken();
   if (FormatTok->Tok.isOneOf(tok::kw_constexpr, tok::identifier))
     nextToken();
   if (FormatTok->Tok.is(tok::l_paren))
     parseParens();
+  // handle  AttributeMacro  if (x) UNLIKELY
+  if (FormatTok->is(TT_AttributeMacro))
+    nextToken();
   // handle [[likely]] / [[unlikely]]
   if (FormatTok->is(tok::l_square) && tryToParseSimpleAttribute())
     parseSquare();
   bool NeedsUnwrappedLine = false;
   if (FormatTok->Tok.is(tok::l_brace)) {
     CompoundStatementIndenter Indenter(this, Style, Line->Level);
     parseBlock();
     if (Style.BraceWrapping.BeforeElse)
       addUnwrappedLine();
     else
       NeedsUnwrappedLine = true;
   } else {
     addUnwrappedLine();
     ++Line->Level;
     parseStructuralElement();
     --Line->Level;
   }
   if (FormatTok->Tok.is(tok::kw_else)) {
     nextToken();
+    // handle  AttributeMacro  else UNLIKELY
+    if (FormatTok->is(TT_AttributeMacro))
+      nextToken();
     // handle [[likely]] / [[unlikely]]
     if (FormatTok->Tok.is(tok::l_square) && tryToParseSimpleAttribute())
       parseSquare();
     if (FormatTok->Tok.is(tok::l_brace)) {
       CompoundStatementIndenter Indenter(this, Style, Line->Level);
       parseBlock();
       addUnwrappedLine();
     } else if (FormatTok->Tok.is(tok::kw_if)) {

clang/unittests/Format/FormatTest.cpp

verifyFormat("if (argc > 5) [[unlikely]] {\n"
                "  return 42;\n"
                "}\n",
                Style);
 
   verifyFormat("if (argc > 5) [[gnu::unused]] {\n"
                "  return 29;\n"
                "}",
                Style);
+
+  verifyFormat("if (argc > 5) [[unlikely]]\n"
+               "  return 29;\n",
+               Style);
+  verifyFormat("if (argc > 5) [[likely]]\n"
+               "  return 29;\n",
+               Style);
+
+  Style.AttributeMacros.push_back("UNLIKELY");
+  Style.AttributeMacros.push_back("LIKELY");
+  verifyFormat("if (argc > 5) UNLIKELY\n"
+               "  return 29;\n",
+               Style);
+
+  verifyFormat("if (argc > 5) UNLIKELY {\n"
+               "  return 29;\n"
+               "}",
+               Style);
+  verifyFormat("if (argc > 5) UNLIKELY {\n"
+               "  return 29;\n"
+               "} else [[likely]] {\n"
+               "  return 42;\n"
+               "}\n",
+               Style);
+  verifyFormat("if (argc > 5) UNLIKELY {\n"
+               "  return 29;\n"
+               "} else LIKELY {\n"
+               "  return 42;\n"
+               "}\n",
+               Style);
+  verifyFormat("if (argc > 5) [[unlikely]] {\n"
+               "  return 29;\n"
+               "} else LIKELY {\n"
+               "  return 42;\n"
+               "}\n",
+               Style);
 }
 
 TEST_F(FormatTest, PenaltyIndentedWhitespace) {
   verifyFormat("Constructor()\n"
                "    : aaaaaa(aaaaaa), aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(\n"
                "                          aaaa(aaaaaaaaaaaaaaaaaa, "
                "aaaaaaaaaaaaaaaaaat))");
   verifyFormat("Constructor()\n"