THRIFT-4717: fix up make clean with autoconf
diff --git a/lib/dart/Makefile.am b/lib/dart/Makefile.am
index ab6ddc0..373a883 100644
--- a/lib/dart/Makefile.am
+++ b/lib/dart/Makefile.am
@@ -22,12 +22,18 @@
 
 clean-local:
 	$(RM) -r .pub
-	find . -type d -name "packages" | xargs $(RM) -r
+	find . -type d -name ".dart_tool" | xargs $(RM) -r
 	find . -type f -name ".packages" | xargs $(RM)
-	find . -type f -name "pubspec.lock" | xargs $(RM)
+	find . -type d -name "packages" | xargs $(RM) -r
 
 check-local: all
 
+dist-hook:
+	$(RM) -r $(distdir)/.pub
+	find $(distdir) -type d -name ".dart_tool" | xargs $(RM) -r
+	find $(distdir) -type f -name ".packages" | xargs $(RM)
+	find $(distdir) -type d -name "packages" | xargs $(RM) -r
+
 EXTRA_DIST = \
 	.analysis_options