maint: update to latest gnulib

Among other patches, Natanael Copa contributed a fix for
pyshmem_available when using musl libc that directly affects
libvirt.

* .gnulib: Update to latest, in part for musl libc compat.

Signed-off-by: Eric Blake <eblake@redhat.com>

diff --git a/.gnulib b/.gnulib
index ce457d622d947d8aa3e325d98a2818d097e7fec9..e8e0eb6bfb728685ec8d5afd924e41b18e9d928d 160000 (submodule)
--- a/.gnulib
+++ b/.gnulib
@@ -1 +1 @@
-Subproject commit ce457d622d947d8aa3e325d98a2818d097e7fec9
+Subproject commit e8e0eb6bfb728685ec8d5afd924e41b18e9d928d