[NFC][clang][PCH][ObjC] Add some missing `VisitStmt(S);`

[lebedev.ri]

Summary

These ObjC AST classes inherit from Stmt, but don't call VisitStmt(S);.
Some were founded with help of existing tests (with NumStmtFields bumped to 1),
but some of them don't even have PCH test coverage. :/

[aprantl]

How can this change be NFC?

[lebedev.ri]

In D59197#1424644, @aprantl wrote:

How can this change be NFC?

VisitStmt() is empty currently, there is currently no data serialized by the Stmt itself.
D59214 changes that.

[jordan_rose]

I'm no Clang serialization expert but this makes sense to me. It's consistent with all the other statement visitor methods.

[lebedev.ri]

In D59197#1424832, @jordan_rose wrote:

I'm no Clang serialization expert but this makes sense to me. It's consistent with all the other statement visitor methods.

Thank you.

lib/Serialization/ASTReaderStmt.cpp

 
 void ASTStmtReader::VisitObjCAtFinallyStmt(ObjCAtFinallyStmt *S) {
   VisitStmt(S);
   S->setFinallyBody(Record.readSubStmt());
   S->setAtFinallyLoc(ReadSourceLocation());
 }
 
 void ASTStmtReader::VisitObjCAutoreleasePoolStmt(ObjCAutoreleasePoolStmt *S) {
-  VisitStmt(S);
+  VisitStmt(S); // FIXME: no test coverage.
   S->setSubStmt(Record.readSubStmt());
   S->setAtLoc(ReadSourceLocation());
 }
 
 void ASTStmtReader::VisitObjCAtTryStmt(ObjCAtTryStmt *S) {
   VisitStmt(S);
   assert(Record.peekInt() == S->getNumCatchStmts());
   Record.skipInts(1);
   bool HasFinally = Record.readInt();
   S->setTryBody(Record.readSubStmt());
   for (unsigned I = 0, N = S->getNumCatchStmts(); I != N; ++I)
     S->setCatchStmt(I, cast_or_null<ObjCAtCatchStmt>(Record.readSubStmt()));
 
   if (HasFinally)
     S->setFinallyStmt(Record.readSubStmt());
   S->setAtTryLoc(ReadSourceLocation());
 }
 
 void ASTStmtReader::VisitObjCAtSynchronizedStmt(ObjCAtSynchronizedStmt *S) {
-  VisitStmt(S);
+  VisitStmt(S); // FIXME: no test coverage.
   S->setSynchExpr(Record.readSubStmt());
   S->setSynchBody(Record.readSubStmt());
   S->setAtSynchronizedLoc(ReadSourceLocation());
 }
 
 void ASTStmtReader::VisitObjCAtThrowStmt(ObjCAtThrowStmt *S) {
-  VisitStmt(S);
+  VisitStmt(S); // FIXME: no test coverage.
   S->setThrowExpr(Record.readSubStmt());
   S->setThrowLoc(ReadSourceLocation());
 }
 
 void ASTStmtReader::VisitObjCBoolLiteralExpr(ObjCBoolLiteralExpr *E) {
   VisitExpr(E);
   E->setValue(Record.readInt());
   E->setLocation(ReadSourceLocation());

lib/Serialization/ASTWriterStmt.cpp

void ASTStmtWriter::VisitObjCForCollectionStmt(ObjCForCollectionStmt *S) {
   Record.AddStmt(S->getCollection());
   Record.AddStmt(S->getBody());
   Record.AddSourceLocation(S->getForLoc());
   Record.AddSourceLocation(S->getRParenLoc());
   Code = serialization::STMT_OBJC_FOR_COLLECTION;
 }
 
 void ASTStmtWriter::VisitObjCAtCatchStmt(ObjCAtCatchStmt *S) {
+  VisitStmt(S);
   Record.AddStmt(S->getCatchBody());
   Record.AddDeclRef(S->getCatchParamDecl());
   Record.AddSourceLocation(S->getAtCatchLoc());
   Record.AddSourceLocation(S->getRParenLoc());
   Code = serialization::STMT_OBJC_CATCH;
 }
 
 void ASTStmtWriter::VisitObjCAtFinallyStmt(ObjCAtFinallyStmt *S) {
+  VisitStmt(S);
   Record.AddStmt(S->getFinallyBody());
   Record.AddSourceLocation(S->getAtFinallyLoc());
   Code = serialization::STMT_OBJC_FINALLY;
 }
 
 void ASTStmtWriter::VisitObjCAutoreleasePoolStmt(ObjCAutoreleasePoolStmt *S) {
+  VisitStmt(S); // FIXME: no test coverage.
   Record.AddStmt(S->getSubStmt());
   Record.AddSourceLocation(S->getAtLoc());
   Code = serialization::STMT_OBJC_AUTORELEASE_POOL;
 }
 
 void ASTStmtWriter::VisitObjCAtTryStmt(ObjCAtTryStmt *S) {
+  VisitStmt(S);
   Record.push_back(S->getNumCatchStmts());
   Record.push_back(S->getFinallyStmt() != nullptr);
   Record.AddStmt(S->getTryBody());
   for (unsigned I = 0, N = S->getNumCatchStmts(); I != N; ++I)
     Record.AddStmt(S->getCatchStmt(I));
   if (S->getFinallyStmt())
     Record.AddStmt(S->getFinallyStmt());
   Record.AddSourceLocation(S->getAtTryLoc());
   Code = serialization::STMT_OBJC_AT_TRY;
 }
 
 void ASTStmtWriter::VisitObjCAtSynchronizedStmt(ObjCAtSynchronizedStmt *S) {
+  VisitStmt(S); // FIXME: no test coverage.
   Record.AddStmt(S->getSynchExpr());
   Record.AddStmt(S->getSynchBody());
   Record.AddSourceLocation(S->getAtSynchronizedLoc());
   Code = serialization::STMT_OBJC_AT_SYNCHRONIZED;
 }
 
 void ASTStmtWriter::VisitObjCAtThrowStmt(ObjCAtThrowStmt *S) {
+  VisitStmt(S); // FIXME: no test coverage.
   Record.AddStmt(S->getThrowExpr());
   Record.AddSourceLocation(S->getThrowLoc());
   Code = serialization::STMT_OBJC_AT_THROW;
 }
 
 void ASTStmtWriter::VisitObjCBoolLiteralExpr(ObjCBoolLiteralExpr *E) {
   VisitExpr(E);
   Record.push_back(E->getValue());