Update libgsystem

This ensures we're disting the README, which makes the autogen.sh do
the right thing.

diff --git a/src/libgsystem b/src/libgsystem
index 5ed135b8f56a4a7d085a7fa144fdc59131ba8d51..c6b949b3ddd1c214db15a31ccdbdff70aa01fa26 160000 (submodule)
--- a/src/libgsystem
+++ b/src/libgsystem
@@ -1 +1 @@
-Subproject commit 5ed135b8f56a4a7d085a7fa144fdc59131ba8d51
+Subproject commit c6b949b3ddd1c214db15a31ccdbdff70aa01fa26