[Attributes] Improve writing `ExprArgument` value.

[vsapsai]

Summary

Instead of dumping Expr* memory address, output Expr representation.

[aaron.ballman]

LGTM!

[vsapsai]

Thanks for the review!

clang/test/SemaCXX/attr-print.cpp

 // CHECK: class __single_inheritance SingleInheritance;
 class __single_inheritance SingleInheritance;
 
 // CHECK: class __multiple_inheritance MultipleInheritance;
 class __multiple_inheritance MultipleInheritance;
 
 // CHECK: class __virtual_inheritance VirtualInheritance;
 class __virtual_inheritance VirtualInheritance;
+
+// CHECK: typedef double *aligned_double __attribute__((align_value(64)));
+typedef double * __attribute__((align_value(64))) aligned_double;

clang/utils/TableGen/ClangAttrEmitter.cpp

void writeTemplateInstantiation(raw_ostream &OS) const override {
       OS << "        ExprResult " << "Result = S.SubstExpr("
          << "A->get" << getUpperName() << "(), TemplateArgs);\n";
       OS << "        if (Result.isInvalid())\n";
       OS << "          return nullptr;\n";
       OS << "        tempInst" << getUpperName() << " = Result.get();\n";
       OS << "      }\n";
     }
 
+    void writeValue(raw_ostream &OS) const override {
+      OS << "\";\n";
+      OS << "    get" << getUpperName()
+         << "()->printPretty(OS, nullptr, Policy);\n";
+      OS << "    OS << \"";
+    }
+
     void writeDump(raw_ostream &OS) const override {}
 
     void writeDumpChildren(raw_ostream &OS) const override {
       OS << "    Visit(SA->get" << getUpperName() << "());\n";
     }
 
     void writeHasChildren(raw_ostream &OS) const override { OS << "true"; }
   };