The moved-from location checks for the existence of whether certain
generators are needed for any target in a loop, rather than whether
the current target has an install rule.

This was introduced in commit v3.4.0-rc1~275^2~3 (cmInstallCommand: Move
the SetHaveInstallRule invocation., 2015-07-28).  Move the
SetHaveInstallRule call to a more-obvious place where the
cmInstallTargetGenerator is constructed.