The --force-interactive option was introduced in SVN 1.8, and trying to
pass it to older SVN clients causes an error; CentOS 7 includes SVN 1.7,
for example, so this makes git llvm not usable out of the box. Older
clients would be interactive by default anyway , so just don't pass
the option if it's not supported.
An alternative would be to check the version instead of checking the
help text, but I think directly detecting the presence of the option is