THRIFT-4717: fix up make clean with autoconf
diff --git a/lib/as3/Makefile.am b/lib/as3/Makefile.am
index 5a078c6..0b3c3be 100644
--- a/lib/as3/Makefile.am
+++ b/lib/as3/Makefile.am
@@ -31,6 +31,7 @@
 	./gradlew $(GRADLE_OPTS) clean \
 		-Prelease=true \
                 --console=plain
+	$(RM) -r .gradle
 
 check-local: $(THRIFT)
 	./gradlew $(GRADLE_OPTS) test \
@@ -43,6 +44,9 @@
                 -Psign=true \
 		--console=plain
 
+dist-hook:
+	$(RM) -r $(distdir)/.gradle/
+
 EXTRA_DIST = \
 	CMakeLists.txt \
 	README.md \