runstatedir was added in yet-to-be released autoconf 2.70. Some distros
are shipping this addition in their autoconf packages, but others, such as Fedora,
are not. This causes the rundir variable to be set incorrectly if the configure script
is regenerated with an unpatched autoconf since the runstatedir variable set is deleted
after regeneration. This change works around that problem by checking that runstatedir
is non-empty before potentially using it to set the rundir variable
92e5d81943