* gnu/packages/base.scm (glibc/linux): Update to 2.26.
[source](patches): Remove 'glibc-memchr-overflow-i686.patch',
'glibc-o-largefile.patch', 'glibc-vectorized-strcspn-guards.patch,
'glibc-CVE-2017-1000366-pt1.patch', 'glibc-CVE-2017-1000366-pt2.patch' and
'glibc-CVE-2017-1000366-pt3.patch'.
(glibc-2.25): New public variable.