[Concepts] Add FoundDecl to ConceptSpecializationExpr serialization

FoundDecl was missing from ConceptSpecializationExpr serialization - add it.

(cherry picked from commit f9e6389)

Author: saarraz

clang/lib/Serialization/ASTReaderStmt.cpp

@@ -754,6 +754,7 @@ void ASTStmtReader::VisitConceptSpecializationExpr(
   E->TemplateKWLoc = Record.readSourceLocation();
   E->ConceptName = Record.readDeclarationNameInfo();
   E->NamedConcept = readDeclAs<ConceptDecl>();
+  E->FoundDecl = Record.readDeclAs<NamedDecl>();
   E->ArgsAsWritten = Record.readASTTemplateArgumentListInfo();
   llvm::SmallVector<TemplateArgument, 4> Args;
   for (unsigned I = 0; I < NumTemplateArgs; ++I)

clang/lib/Serialization/ASTWriterStmt.cpp

@@ -429,6 +429,7 @@ void ASTStmtWriter::VisitConceptSpecializationExpr(
   Record.AddSourceLocation(E->getTemplateKWLoc());
   Record.AddDeclarationNameInfo(E->getConceptNameInfo());
   Record.AddDeclRef(E->getNamedConcept());
+  Record.AddDeclRef(E->getFoundDecl());
   Record.AddASTTemplateArgumentListInfo(E->getTemplateArgsAsWritten());
   for (const TemplateArgument &Arg : TemplateArgs)
     Record.AddTemplateArgument(Arg);