[Clang][TableGen] Add explicit symbol visibility macros to code generated (#109362)

Update ClangAttrEmitter TableGen to add explicit symbol visibility
macros to attribute class declarations it creates.
Both AnnotateFunctions and Attribute example plugins require
clang::AnnotateAttr TableGen created functions to be exported from the
Clang shared library.
This depends on macros to be added in
#108276

Author: fsfod

clang/utils/TableGen/ClangAttrEmitter.cpp

@@ -2727,7 +2727,8 @@ static void emitAttributes(const RecordKeeper &Records, raw_ostream &OS,
     }
 
     if (Header)
-      OS << "class " << R.getName() << "Attr : public " << SuperName << " {\n";
+      OS << "class CLANG_ABI " << R.getName() << "Attr : public " << SuperName
+         << " {\n";
     else
       OS << "\n// " << R.getName() << "Attr implementation\n\n";
 
@@ -3185,7 +3186,8 @@ void clang::EmitClangAttrClass(const RecordKeeper &Records, raw_ostream &OS) {
   emitSourceFileHeader("Attribute classes' definitions", OS, Records);
 
   OS << "#ifndef LLVM_CLANG_ATTR_CLASSES_INC\n";
-  OS << "#define LLVM_CLANG_ATTR_CLASSES_INC\n\n";
+  OS << "#define LLVM_CLANG_ATTR_CLASSES_INC\n";
+  OS << "#include \"clang/Support/Compiler.h\"\n\n";
 
   emitAttributes(Records, OS, true);