Ensure -lm is on the libmaestro.la dependency list if needed

Makefile.am

@@ -60,7 +60,8 @@ libmaestro_la_LIBADD = 			 \
 	protocols/libmaestro_proto.la \
 	transport/libmaestro_transport.la \
 	transformation/libmaestro_transformation.la \
-	attributes/libattributes.la
+	attributes/libattributes.la \
+	$(LIBS)
 
 # README
 dist_doc_DATA = README.md