Test for verto_set_flags in system libverto

libkrad relies on verto_set_flags, which was added to libverto in
release 0.2.4.  Make sure the system libverto has this function before
choosing it over the built-in version.

(cherry picked from commit a47d639770f32418c6e3fa8a0503019c9b376d2a)

https://github.com/krb5/krb5/commit/d08778489c7510e5e6bc27306ab68706fcaf222f
Author: Greg Hudson <ghudson@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: d08778489c7510e5e6bc27306ab68706fcaf222f
Branch: krb5-1.12
 src/configure.in |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)