In commit d7679f6427 (QCMakeCacheView: use non-deprecated List and Set
constructions, 2020-06-10, v3.18.0-rc2~13^2) the conversion of the
`this->properties()` value to QSet is incorrect for Qt 5.14+. The
problem is that `this->properties()` returns by value, so the range
`this->properties().begin(), this->properties().end()` provides
iterators to two different instances. Use an intermediate temporary
copy of the value to get a consistent iterator range.
Fixes: #20981
af6cf586f6
