[clang][NFC] Pack LambdaExpr

This saves sizeof(void *) bytes per LambdaExpr.

Review-after-commit since this is a straightforward change similar
to the work done on other nodes. NFC.
diff --git a/clang/lib/Serialization/ASTReaderStmt.cpp b/clang/lib/Serialization/ASTReaderStmt.cpp
index 86895c3..e38c309 100644
--- a/clang/lib/Serialization/ASTReaderStmt.cpp
+++ b/clang/lib/Serialization/ASTReaderStmt.cpp
@@ -1687,12 +1687,13 @@
 void ASTStmtReader::VisitLambdaExpr(LambdaExpr *E) {
   VisitExpr(E);
   unsigned NumCaptures = Record.readInt();
-  assert(NumCaptures == E->NumCaptures);(void)NumCaptures;
+  (void)NumCaptures;
+  assert(NumCaptures == E->LambdaExprBits.NumCaptures);
   E->IntroducerRange = readSourceRange();
-  E->CaptureDefault = static_cast<LambdaCaptureDefault>(Record.readInt());
+  E->LambdaExprBits.CaptureDefault = Record.readInt();
   E->CaptureDefaultLoc = readSourceLocation();
-  E->ExplicitParams = Record.readInt();
-  E->ExplicitResultType = Record.readInt();
+  E->LambdaExprBits.ExplicitParams = Record.readInt();
+  E->LambdaExprBits.ExplicitResultType = Record.readInt();
   E->ClosingBrace = readSourceLocation();
 
   // Read capture initializers.