With the recent release of Perl 5.26.0, this warning has become an error, so automake doesn't work at all on any packages. For example, with libvncserver-0.9.11 (which doesn't provide any release tarball with pregenerated autotools):
...
autoreconf: running: automake --add-missing --copy
Unescaped left brace in regex is illegal here in regex; marked by <--
HERE in m/\${ <-- HERE ([6 \t=:={}]+)}/ at /usr/bin/automake line
3936.
autoreconf: automake failed with exit status: 255
--
Daniel Schepler
