[c++20] Add CXXRewrittenBinaryOperator to represent a comparison
operator that is rewritten as a call to multiple other operators.

No functionality change yet: nothing creates these expressions.

llvm-svn: 375305
diff --git a/clang/lib/Serialization/ASTWriterStmt.cpp b/clang/lib/Serialization/ASTWriterStmt.cpp
index 84a5324..c39d4d3 100644
--- a/clang/lib/Serialization/ASTWriterStmt.cpp
+++ b/clang/lib/Serialization/ASTWriterStmt.cpp
@@ -1375,6 +1375,14 @@
   Code = serialization::EXPR_CXX_MEMBER_CALL;
 }
 
+void ASTStmtWriter::VisitCXXRewrittenBinaryOperator(
+    CXXRewrittenBinaryOperator *E) {
+  VisitExpr(E);
+  Record.push_back(E->isReversed());
+  Record.AddStmt(E->getSemanticForm());
+  Code = serialization::EXPR_CXX_REWRITTEN_BINARY_OPERATOR;
+}
+
 void ASTStmtWriter::VisitCXXConstructExpr(CXXConstructExpr *E) {
   VisitExpr(E);