Walter Gray authored Jun 05, 2017 and Brad King committed Jun 06, 2017

The change in commit v3.9.0-rc1~6^2~1 (C++ feature checks: check output
for '[Ww]arning', 2017-06-03) accidentally matches `0 Warning(s)` in the
output and always thinks a warning exists, thus failing all checks in
Visual Studio builds.

Fixes: #16942