// The legacy PM CGPassManager discovers SCCs this way: for function in the source order tarjanSCC(function) // While the new PM CGSCCPassManager does: for function in the reversed source order  discover a reference graph SCC build call graph SCCs inside the reference graph SCC
In the common cases, reference graph ~= call graph, the new PM order is
undesired because for a | b | c (3 independent functions), the new PM will
process them in the reversed order: c, b, a. If a <-> b <-> c, we can see
that -print-after-all will report the sole SCC as scc: (c, b, a).
This patch corrects the iteration order . The discovered SCC order will match
the legacy PM in the common cases.
For some tests (Transforms/Inline/cgscc-*.ll and
unittests/Analysis/CGSCCPassManagerTest.cpp), the behaviors are dependent on
the SCC discovery order and there are too many check lines for the particular
order. This patch simply reverses the function order to avoid change too many