[clang-format] Avoid adding space after the name of a function-like macro when the name is a keyword.

[curdeius]

Summary

Fixes https://github.com/llvm/llvm-project/issues/31086.

Before the code:

#define if(x)

was erroneously formatted to:

#define if (x)

clang/lib/Format/UnwrappedLineParser.cpp

if (IncludeGuard == IG_IfNdefed &&
     for (auto &Line : Lines) {
       if (!Line.Tokens.front().Tok->isOneOf(tok::comment, tok::hash)) {
         IncludeGuard = IG_Rejected;
         break;
       }
     }
   }
 
+  // In the context of a define, even keywords should be treated as normal
+  // identifiers. Setting the kind to identifier is not enough, because we need
+  // to treat additional keywords like __except as well, which are already
+  // identifiers.
+  FormatTok->Tok.setKind(tok::identifier);
+  FormatTok->Tok.setIdentifierInfo(nullptr);
   nextToken();
   if (FormatTok->Tok.getKind() == tok::l_paren &&
       !FormatTok->hasWhitespaceBefore())
     parseParens();
   if (Style.IndentPPDirectives != FormatStyle::PPDIS_None)
     Line->Level += PPBranchLevel + 1;
   addUnwrappedLine();
   ++Line->Level;

clang/unittests/Format/FormatTest.cpp

TEST_F(FormatTest, FormatShortBracedStatements) {
   verifyFormat("BOOST_FOREACH (int v, vec) {}", AllowSimpleBracedStatements);
   verifyFormat("BOOST_FOREACH (int v, vec)\n"
                "{\n"
                "  f();\n"
                "}",
                AllowSimpleBracedStatements);
 }
 
+TEST_F(FormatTest, UnderstandsMacros) {
+  verifyFormat("#define A (parentheses)");
+  verifyFormat("#define true ((int)1)");
+  verifyFormat("#define and(x)");
+  verifyFormat("#define if(x) x");
+  verifyFormat("#define return(x) (x)");
+  verifyFormat("#define while(x) for (; x;)");
+  verifyFormat("#define xor(x) (^(x))");
+  verifyFormat("#define __except(x)");
+  verifyFormat("#define __try(x)");
+}
+
 TEST_F(FormatTest, ShortBlocksInMacrosDontMergeWithCodeAfterMacro) {
   FormatStyle Style = getLLVMStyleWithColumns(60);
   Style.AllowShortBlocksOnASingleLine = FormatStyle::SBS_Always;
   Style.AllowShortIfStatementsOnASingleLine = FormatStyle::SIS_WithoutElse;
   Style.BreakBeforeBraces = FormatStyle::BS_Allman;
   EXPECT_EQ("#define A                                                  \\\n"
             "  if (HANDLEwernufrnuLwrmviferuvnierv)                     \\\n"
             "  {                                                        \\\n"