Subject: Unescaped left brace in regex is deprecated, passed through in regex

From: carl hansen <[email-masked]>
Date: Sun, 22 May 2016 23:23:23 -0700

>> automake --version
Unescaped left brace in regex is deprecated, passed through in regex;
marked by <-- HERE in m/\${ <-- HERE ([^ \t=:+{}]+)}/ at
/opt/gsrc/bin/automake line 3936.
automake (GNU automake) 1.15
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv2+: GNU GPL version 2 or later ....

using perl 5.22.1

how to fix ?