This function calculates the topological order of variables.
We will use it to determine which and in what order to link
module libraries.
The function is not tied to libraries/modules only, but requires
the variables to be ordered to have their dependencies in the
[prefix]<var>.depends subvariable.
Due to the recursive nature of the algorithm it was just much easier
to implement it directly in C++ rather than in a qmake-language
function.
This is the beginning of revision history for this module. If you
want to look at revision history older than this, please refer to the
Qt Git wiki for how to use Git history grafting. At the time of
writing, this wiki is located here:
http://qt.gitorious.org/qt/pages/GitIntroductionWithQt
If you have already performed the grafting and you don't see any
history beyond this commit, try running "git log" with the "--follow"
argument.
Branched from the monolithic repo, Qt master branch, at commit
896db169ea224deb96c59ce8af800d019de63f12
