glibc: fix CVE-2020-27618

iconv: Accept redundant shift sequences in IBM1364

Reference:
https://bugzilla.redhat.com/show_bug.cgi?id=1893708



Signed-off-by: Yi Fan Yu <yifan.yu@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>