[Clang] Fix build with GCC 14 on ARM (#78704)gentoo-17.0.6-r1

GCC 14 defines `__arm_streaming` as a macro expanding to
`[[arm::streaming]]`. Due to the nested macro use, this gets expanded
prior to concatenation.

It doesn't look like C++ has a really clean way to prevent macro
expansion. The best I have found is to use `EMPTY ## X` where `EMPTY` is
an empty macro argument, so this is the hack I'm implementing here.

Fixes https://github.com/llvm/llvm-project/issues/78691.

Rebased for 17.x by Michał Górny.

Gentoo-Component: clang

3 files changed, 4 insertions, 3 deletions

diff --git a/clang/include/clang/Basic/TokenKinds.def b/clang/include/clang/Basic/TokenKinds.def
index ef0dad0f2dcd..3add13c079f3 100644
--- a/clang/include/clang/Basic/TokenKinds.def
+++ b/clang/include/clang/Basic/TokenKinds.def
@@ -752,8 +752,9 @@ KEYWORD(__builtin_available              , KEYALL)
 KEYWORD(__builtin_sycl_unique_stable_name, KEYSYCL)
 
 // Keywords defined by Attr.td.
+// The "EMPTY ## X" is used to prevent early macro-expansion of the keyword.
 #ifndef KEYWORD_ATTRIBUTE
-#define KEYWORD_ATTRIBUTE(X) KEYWORD(X, KEYALL)
+#define KEYWORD_ATTRIBUTE(X, EMPTY) KEYWORD(EMPTY ## X, KEYALL)
 #endif
 #include "clang/Basic/AttrTokenKinds.inc"
 
diff --git a/clang/include/clang/Basic/TokenKinds.h b/clang/include/clang/Basic/TokenKinds.h
index e4857405bc7f..ff117bd5afc5 100644
--- a/clang/include/clang/Basic/TokenKinds.h
+++ b/clang/include/clang/Basic/TokenKinds.h
@@ -109,7 +109,7 @@ bool isPragmaAnnotation(TokenKind K);
 
 inline constexpr bool isRegularKeywordAttribute(TokenKind K) {
   return (false
-#define KEYWORD_ATTRIBUTE(X) || (K == tok::kw_##X)
+#define KEYWORD_ATTRIBUTE(X, ...) || (K == tok::kw_##X)
 #include "clang/Basic/AttrTokenKinds.inc"
   );
 }
diff --git a/clang/utils/TableGen/ClangAttrEmitter.cpp b/clang/utils/TableGen/ClangAttrEmitter.cpp
index b5813c6abc2b..79db17501b64 100644
--- a/clang/utils/TableGen/ClangAttrEmitter.cpp
+++ b/clang/utils/TableGen/ClangAttrEmitter.cpp
@@ -3430,7 +3430,7 @@ void EmitClangAttrTokenKinds(RecordKeeper &Records, raw_ostream &OS) {
                      "RegularKeyword attributes with arguments are not "
                      "yet supported");
         OS << "KEYWORD_ATTRIBUTE("
-           << S.getSpellingRecord().getValueAsString("Name") << ")\n";
+           << S.getSpellingRecord().getValueAsString("Name") << ", )\n";
       }
   OS << "#undef KEYWORD_ATTRIBUTE\n";
 }