tree-optimization/115599 - reassoc qsort comparator issue

tree-optimization/115599 - reassoc qsort comparator issue

The compare_repeat_factors comparator fails qsort checking eventually
because it uses rf2->rank - rf1->rank to compare unsigned numbers
which causes issues for ranks that interpret negative as signed.

Fixed by re-writing the obvious way.  I've also fixed the count
comparison which suffers from truncation as count is 64bit signed
while the comparator result is 32bit int (that's a lot less likely
to hit in practice though).

The testcase from the PR is too large to include.

	PR tree-optimization/115599
	* tree-ssa-reassoc.cc (compare_repeat_factors): Use explicit
	compares to avoid truncations.