maint: update gnulib

* Jump 867 commits a head from b9bfe78424b87 to d3181471f95c8.
* build-aux/.gitignore: Add file from gnulib to ignore list.
* doc/.gitignore: Likewise.

diff --git a/build-aux/.gitignore b/build-aux/.gitignore
line changes: +1/-0
index b077960..e6835de
--- a/build-aux/.gitignore
+++ b/build-aux/.gitignore

@@ -1,4 +1,5 @@
 /announce-gen
+/ar-lib
 /compile
 /config.guess
 /config.rpath

diff --git a/doc/.gitignore b/doc/.gitignore
line changes: +1/-0
index 5771373..cc78a11
--- a/doc/.gitignore
+++ b/doc/.gitignore

@@ -1,3 +1,4 @@
 /fdl.texi
 /version.texi
 /gendocs_template
+/gendocs_template_min

diff --git a/gnulib b/gnulib
line changes: +1/-1
index b9bfe78..d318147
--- a/gnulib
+++ b/gnulib

@@ -1 +1 @@
-Subproject commit b9bfe78424b871f5b92e5ee9e7d21ef951a6801d
+Subproject commit d3181471f95c870e9485be947608be84f7fe5325