Update build-aux to current.

diff --git a/build-aux b/build-aux
index e29d336..53fba0e 160000 (submodule)
--- a/build-aux
+++ b/build-aux
@@ -1 +1 @@
-Subproject commit e29d336021160ae1dfea0d0c9316b79900d33a70
+Subproject commit 53fba0e052502d7192bacdcef1bd8a51b066686b