build: update from gnulib

* gnulib: Update submodule to latest.

diff --git a/gnulib b/gnulib
index 12f78b4faa14cd2da952f865979843dee79fcf93..af26ae76eac3e090743d3effefb50dad4c19c1b4 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 12f78b4faa14cd2da952f865979843dee79fcf93
+Subproject commit af26ae76eac3e090743d3effefb50dad4c19c1b4